Pulsed radiofrequency ablation

ABSTRACT

Ablation systems and methods of the present disclosure are directed toward delivering pulsed radiofrequency (RF) energy to target tissue. The pulsations of the RF energy, combined with cooling at a surface of the target tissue, can advantageously promote local heat transfer in the target tissue to form lesions having dimensions larger than those that can be safely formed in tissue using non-pulsed RF energy under similar conditions.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit under 35 U.S.C. §119(e) of U.S.Prov. App. No. 62/330,395, filed May 2, 2016, U.S. Prov. App. No.62/357,704, filed Jul. 1, 2016, U.S. Prov. App. No. 62/399,632, filedSep. 26, 2016, U.S. Prov. App. No. 62/399,625, filed Sep. 26, 2016, U.S.Prov. App. No. 62/420,610, filed Nov. 11, 2016, U.S. Prov. App. No.62/424,736, filed Nov. 21, 2016, U.S. Prov. App. No. 62/428,406, filedNov. 30, 2016, U.S. Prov. App. No. 62/434,073, filed Dec. 14, 2016, U.S.Prov. App. No. 62/468,339, filed Mar. 7, 2017, and U.S. Prov. App. No.62/468,873, filed Mar. 8, 2017, with the entire contents of each ofthese applications hereby incorporated herein by reference.

This application is also related to the following commonly-owned U.S.patent applications filed on even date herewith: Attorney Docket NumberAFRA-0001-P01, entitled “CATHETER SENSING AND IRRIGATING”; AttorneyDocket Number AFRA-0009-P01, entitled “LESION FORMATION”; AttorneyDocket Number AFRA-00011-P01, entitled “THERAPEUTIC CATHETER WITHIMAGING”; and Attorney Docket Number AFRA-0013-P01, entitled “CATHETERINSERTION.” Each of the foregoing applications is hereby incorporatedherein by reference in its entirety.

BACKGROUND

Abnormal rhythms generally referred to as arrhythmia can occur in theheart. Cardiac arrhythmias develop when abnormal conduction in themyocardial tissue modifies the typical heartbeat pattern. Radiofrequency (“RF”) catheter ablation can be used to form lesions thatinterrupt the mechanism of abnormal conduction to terminate certainarrhythmias.

SUMMARY

Ablation systems and methods of the present disclosure are directedtoward delivering pulsed radiofrequency (RF) energy to target tissue.The pulsations of the RF energy, combined with cooling at a surface ofthe target tissue, can advantageously promote local heat transfer in thetarget tissue to form lesions having dimensions larger than those thatcan be safely formed in tissue using non-pulsed RF energy under similarconditions.

According to one aspect, a method includes placing an ablation electrodeat an interface between tissue and blood in an anatomic structure of apatient, delivering RF energy to the ablation electrode at the interfaceduring a period of lesion formation, and delivering an irrigation fluidto the interface during at least a portion of the period of lesionformation. The RF energy delivered to the ablation electrode at theinterface is pulsed to cycle between a first energy phase and a secondenergy phase during the period of lesion formation, the RF energy in thefirst energy phase being greater than the RF energy in the second energyphase, and a combination of irrigation fluid and blood moves through theablation electrode to cool the ablation electrode at the interfaceduring the period of lesion formation.

In certain implementations, a rate of cooling of the interface by thecombination of blood and irrigation fluid moving through the ablationelectrode at the interface is greater than a rate of heating of theinterface by the RF energy during the second energy phase.

In some implementations, the second energy phase can be an off phase.

In certain implementations, during each second energy phase, tissue atthe interface can undergo more cooling than tissue at a depth from theinterface.

In some implementations, during the period of lesion formation, the RFenergy can be cycled between at least two cycles, with each cycleincluding a second energy phase and a first energy phase.

In certain implementations, each second energy phase can have a durationgreater than 0 seconds and less than about 6 seconds.

In some implementations, each second energy phase has a predeterminedduration.

In certain implementations, each first energy phase can have apredetermined duration.

In some implementations, the method can further include receiving, froma temperature sensor disposed at the interface, a signal indicative oftemperature of the interface, wherein a duration of one or more of thefirst energy phase and the second energy phase is based on the signalindicative of temperature of the interface.

In certain implementations, the method can further include detecting achange in an electrical signal associated with the RF energy deliveredto the ablation electrode at the interface, wherein a duration of one ormore of the first energy phase and the second energy phase is based onthe detected change in the electrical signal.

In some implementations, the first phase of the RF energy can be aboutten seconds.

In certain implementations, the period of lesion formation can be about1 minute to about three minutes.

In some implementations, the anatomic structure can be a heart cavity.For example, the tissue can be the endocardium of the heart cavity.

In certain implementations, a volumetric flow rate of the irrigationfluid delivered to the interface can be based on one or more signalsindicative of temperature at the interface. For example, the volumetricflow rate can be decreased in response to the one or more signalsindicative of temperature being below a first predetermined threshold,and the volumetric flow rate is increased in response to the one or moresignals indicative of temperature being above a second predeterminedthreshold. The first predetermined threshold can be, in certaininstances, different from the second predetermined threshold.Additionally, or alternatively, increasing the volumetric flow rate,decreasing the volumetric flow rate, or both can occur over atemperature range corresponding to a range of the one or more signalsindicative of temperature. Further, or instead, the volumetric flow ratecan be increased according to a first predetermined function of the oneor more signals indicative of temperature and the volumetric flow ratecan be decreased according to a second predetermined function of the oneor more signals indicative of temperature. The first predeterminedfunction can be, in certain instances, different from the secondpredetermined function. Additionally, or alternatively, at least one ofthe first predetermined function and the second predetermined functioncan be continuous. Further, or instead, at least one of the firstpredetermined function of the one or more signals indicative oftemperature and the second predetermined function of the one or moresignals indicative of temperature can be discontinuous (e.g., at leastone of the first predetermined function and the second predeterminedfunction can include a respective step change in the volumetric flowrate).

In some implementations, the method can further include receiving, fromrespective sensors disposed along the ablation electrode, a plurality ofsignals indicative of respective sensed temperatures. Increasing thevolumetric flow rate, decreasing the volumetric flow rate, or both canbe based on a signal of the plurality of signals corresponding to amaximum sensed temperature. Additionally, or alternatively, the methodcan further include processing each signal of the plurality of signalsbased on an inverse Laplacian operator, wherein increasing thevolumetric flow rate, decreasing the volumetric flow rate, or both canbe based on a maximum signal of the processed signals.

In certain implementations, a volumetric flow rate of the irrigationfluid delivered to the interface can be based on the RF energy deliveredto the ablation electrode at the interface.

In some implementations, a volumetric flow rate of the irrigation fluidcan be pulsed between a first volumetric flow rate and a secondvolumetric flow rate less than the first volumetric flow rate. Forexample, the volumetric flow rate of the irrigation fluid can be pulsedsubstantially in phase with the pulsation of the RF energy such that thefirst volumetric flow rate can be substantially in phase with the firstenergy phase and the second volumetric flow rate can be substantially inphase with the second energy phase.

In certain implementations, delivering the irrigation fluid to theinterface can include mixing the irrigation fluid with blood movingthrough the ablation electrode at the interface.

In some implementations, the irrigation fluid can be saline.

In certain implementations, placing the ablation electrode at theinterface between the tissue and blood can include moving the ablationelectrode into the anatomic structure through vasculature of thepatient. For example, the ablation electrode can be coupled to a distalportion of a catheter shaft and placing the ablation electrode at theinterface between tissue and blood in the anatomic structure can includemoving the distal portion of the catheter shaft through vasculature ofthe patient and into the anatomic structure.

According to another aspect, a method includes placing an ablationelectrode at an interface between tissue and blood in an anatomicstructure of a patient such that fluid in the anatomic structure movesthrough the ablation electrode placed at the interface, delivering RFenergy to the ablation electrode at the interface during a period oflesion formation, delivering an irrigation fluid to the interface duringat least a portion of the period of lesion formation such that the fluidmoving through the ablation electrode includes the irrigation fluid, andmonitoring tissue at the interface, wherein monitoring tissue at theinterface includes reducing the RF energy and reducing the volumetricflow rate of the irrigation fluid during a measurement phase of theperiod of lesion formation, receiving one or more signals indicative oftemperature at the interface, and determining a temperature at theinterface based on the one or more signals received during themeasurement phase of the period of lesion formation.

In certain implementations, determining the temperature at the interfacecan be further based on the one or more signals received during aportion of the period of lesion formation other than the measurementphase.

In some implementations, the method can further include displaying thedetermined temperature on a graphical user interface.

In certain implementations, the method can further include, based on thedetermined temperature, titrating the RF energy delivered to theablation electrode.

In some implementations, the method can further include adjusting thevolumetric flow rate of the irrigation fluid based on the determinedtemperature.

In some implementations, the volumetric flow rate can be decreased inresponse to the determined temperature being below a first predeterminedthreshold. Additionally, or alternatively volumetric flow rate can beincreased in response to the determined temperature being above a secondpredetermined threshold.

In certain implementations, receiving the one or more signals indicativeof temperature at the interface can include receiving, from respectivesensors disposed along the ablation electrode, a plurality of signalsindicative of a respective plurality of sensed temperatures. Forexample, increasing the volumetric flow rate, decreasing the volumetricflow rate, or both can be based on a signal of the plurality of signalscorresponding to a maximum sensed temperature. Additionally, oralternatively, each signal of the plurality of signals can be based onan inverse Laplacian operator, wherein increasing the volumetric flowrate, decreasing the volumetric flow rate, or both is based on a maximumsignal of the processed signals.

In some implementations, the method can further include increasing theRF energy following reduction of the RF energy, and increasing thevolumetric flow rate of the irrigation fluid following reduction of thevolumetric flow rate of the irrigation fluid.

In certain implementations, the RF energy can be pulsed to cycle betweena first energy phase and a second energy phase during the period oflesion formation, the delivered RF energy in the first energy phase canbe greater than the delivered RF energy in the second energy phase.

According to still another aspect, a method includes placing an ablationelectrode at an interface between tissue and blood in an anatomicstructure of a patient such that fluid in the anatomic structure movesthrough the ablation electrode placed at the interface, delivering RFenergy to the ablation electrode at the interface during a period oflesion formation, delivering an irrigation fluid to the interface duringat least a portion of the period of lesion formation such that the fluidmoving through the ablation electrode includes irrigation fluid, andmonitoring tissue at the interface, wherein monitoring tissue at theinterface includes receiving one or more signals indicative oftemperature at the interface, determining a temperature at the interfacebased on the one or more received signals, and increasing the volumetricflow rate based on the determined temperature exceeding a predeterminedthreshold (e.g., about 55° C.).

According to still another aspect a system includes an ablationelectrode, an irrigation element, a generator, and a controller. Theablation electrode is positionable at an interface between endocardiumtissue and blood in a heart cavity of a patient such that fluid in theheart cavity is movable through the ablation electrode at the interfaceto cool the ablation electrode during a period of lesion formation. Theirrigation element defines at least one orifice positioned to directirrigation fluid toward the ablation electrode such that the fluidmovable through the ablation electrode at the interface includesirrigation fluid. The generator is in electrical communication with theablation electrode to deliver RF energy to the ablation electrode duringthe period of lesion formation. The controller is in communication withthe generator, the controller including one or more processors and anon-transitory, computer-readable storage medium having stored thereoncomputer executable instructions for causing the one or more processorsto control energy delivered from the generator to the ablation electrodeat the interface between the endocardium tissue and blood during theperiod of lesion formation, wherein the RF energy delivered to theablation electrode at the interface is pulsed to alternate between afirst energy phase and a second energy phase during the period of lesionformation, the delivered RF energy in the first energy phase beinggreater than the delivered RF energy in the second energy phase.

In certain implementations, the ablation electrode can be positionableat the interface such that blood is movable through the ablationelectrode at the interface to cool the ablation electrode during theperiod of lesion formation.

In some implementations, the at least one orifice of the irrigationelement can be positioned to direct irrigation fluid toward the ablationelectrode such that the fluid movable past the ablation electrode is amixture of the irrigation fluid and blood in the heart cavity.

In certain implementations, the controller can be in communication witha source of irrigation fluid in fluid communication with the at leastone orifice of the irrigation element to control a volumetric flow rateof irrigation fluid moving from the source of irrigation fluid andthrough the at least one orifice. Additionally, or alternatively, thecomputer executable instructions can further include instructions forcausing the one or more processors to control a volumetric flow rate ofirrigation fluid delivered from the source of irrigation fluid andthrough the at least one orifice. For example, the computer executableinstructions can further include instructions for causing the one ormore processors to control the volumetric flow rate of irrigation fluidbased on the RF energy delivered to the ablation electrode. As anadditional, or alternative example, the computer executable instructionscan further include instructions for causing the one or more processorsto pulse the volumetric flow rate of irrigation fluid between a firstvolumetric flow rate and a second volumetric flow rate less than thefirst volumetric flow rate. As an example, the computer executableinstructions can further include instructions for causing the one ormore processors to pulse the volumetric flow rate of irrigation fluidsubstantially in phase with the pulsation of the RF energy such that thefirst volumetric flow rate is substantially in phase with the firstenergy phase and the second volumetric rate is substantially in phasewith the second energy phase.

In some implementations, each second energy phase can have a durationgreater than 0 seconds and less than about 6 seconds.

In certain implementations, the first energy phase of the RF energy canbe about ten seconds.

In some implementations, the ablation electrode can be movable throughvasculature of the patient and into the heart cavity of the patient. Forexample, the system can further include a catheter including a proximalportion and a distal portion, the ablation electrode coupled to thedistal portion of the catheter.

According to yet another aspect, a system includes an ablationelectrode, at least one sensor, a generator, an irrigation pump, and acontroller. The ablation electrode is positionable at an interfacebetween endocardium tissue and blood in a heart cavity of a patient. Theat least one sensor is disposed along the ablation electrode. Theirrigation element defines at least one orifice positioned to direct anirrigation fluid toward the ablation electrode. The generator is inelectrical communication with the ablation electrode. The irrigationpump is in mechanical communication with a fluid line to deliver theirrigation fluid through the at least one orifice. The controller is incommunication with the generator, the at least one sensor, and theirrigation pump, the controller including one or more processors and anon-transitory, computer-readable storage medium having stored thereoncomputer executable instructions for causing the one or more processorsto deliver RF energy from the generator to the ablation electrode at theinterface between the endocardium tissue and blood during a period oflesion formation, deliver the irrigation fluid to the interface duringat least a portion of the period of lesion formation, reduce the RFenergy and reduce the volumetric flow rate of the irrigation fluidduring a measurement phase of the period of lesion formation, receivefrom the at least one sensor one or more signals indicative oftemperature at the interface, and determine a temperature at theinterface based on the one or more signals received during themeasurement phase of the period of lesion formation.

In certain implementations, the computer executable instructions forcausing the one or more processors to determine the temperature at theinterface further can include instructions for causing the one or moreprocessors to determine the temperature at the interface further basedon the one or more signals received during a portion of the period oflesion formation other than the measurement phase.

In some implementations, the computer executable instructions canfurther include instructions for causing the one or more processors todisplay the determined temperature on a graphical user interface.

In certain implementations, the computer executable instructions canfurther include instructions for causing the one or more processors totitrate the RF energy delivered to the ablation electrode based on thedetermined temperature.

In some implementations, the ablation electrode can be positionable atthe interface such that blood is movable through the ablation electrodeat the interface to cool the ablation electrode during the period oflesion formation.

In certain implementations, the at least one orifice of the irrigationelement can be positioned to direct irrigation fluid toward the ablationelectrode such that the fluid movable through the ablation electrode isa mixture of the irrigation fluid and blood in the heart cavity.

In some implementations, the computer executable instructions canfurther include instructions for causing the one or more processors tocontrol the volumetric flow rate of irrigation fluid based on the RFenergy delivered to the ablation electrode.

In certain implementations, the computer executable instructions canfurther include instructions for causing the one or more processors topulse the volumetric flow rate of irrigation fluid between a firstvolumetric flow rate and a second volumetric flow rate less than thefirst volumetric flow rate.

In some implementations, the RF energy delivered to the ablationelectrode at the interface can be pulsed to alternate between a firstenergy phase and a second energy phase during the period of lesionformation, the delivered RF energy in the first energy phase beinggreater than the delivered RF energy in the second energy phase.Additionally, or alternatively, the computer executable instructions canfurther include instructions for causing the one or more processors topulse the volumetric flow rate of irrigation fluid substantially inphase with the pulsation of the RF energy such that the first volumetricflow rate is substantially in phase with the first energy phase and thesecond volumetric rate is substantially in phase with the second energyphase. For example, each second energy phase can have a duration greaterthan 0 seconds and less than about 6 seconds. Additionally, oralternatively, the first energy phase of the RF energy can be about tenseconds.

According to still another aspect, a system includes an ablationelectrode, at least one sensor, an irrigation pump, a generator, and acontroller. The ablation electrode is positionable at an interfacebetween endocardium tissue and blood in a heart cavity of a patient suchthat fluid in the heart cavity is movable through the ablation electrodeat the interface to cool the ablation electrode during a period oflesion formation. The at least one sensor is disposed along the ablationelectrode. The irrigation element defines at least one orificepositioned to direct irrigation fluid toward the ablation electrode. Thegenerator is in electrical communication with the ablation electrode todeliver RF energy to the ablation electrode during the period of lesionformation. The irrigation pump is in mechanical communication with afluid line to deliver irrigation fluid through the at least one orifice.The controller is in communication with the generator, the at least onesensor, and the irrigation pump, the controller including one or moreprocessors and a non-transitory, computer-readable storage medium havingstored thereon computer executable instructions for causing the one ormore processors to control energy delivered from the generator to theablation electrode at the interface between the endocardium tissue andblood during a period of lesion formation, based on the one or moresignals from the at least one sensor, determine a temperature at theinterface, deliver irrigation fluid to the interface such that the fluidmoving through the ablation electrode includes the irrigation fluid,increase the volumetric flow rate of the irrigation fluid based on thedetermined temperature exceeding a predetermined threshold.

In certain implementations, the computer-executable instructions todeliver irrigation fluid to the interface can include instructions todecrease the volumetric flow rate of the irrigation fluid in response tothe determined temperature being below the predetermined threshold.

In some implementations, the computer-executable instructions to controlenergy delivered from the generator to the ablation electrode caninclude instructions to pulse RF energy to cycle between a first energyphase and a second energy phase during the period of lesion formation,the delivered RF energy in the first energy phase being greater than thedelivered RF energy in the second energy phase.

Other aspects, features, and advantages will be apparent from thedescription and drawings, and from the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic representation of an ablation system during anablation treatment.

FIG. 2 is a perspective view of a catheter of the ablation system ofFIG. 1.

FIG. 3 is a perspective view of a distal end portion of the catheter ofthe ablation system of FIG. 1.

FIG. 4 is a cross-sectional perspective view along cross-section A-A ofFIG. 3.

FIG. 5 is a schematic representation of a jet of irrigation fluid movingfrom an irrigation element to an inner portion of an ablation electrodeof the catheter of FIG. 2.

FIG. 6 is a side view of an ablation electrode of the ablation system ofFIG. 1.

FIG. 7 is a perspective view of the ablation electrode of the ablationsystem of FIG. 1.

FIG. 8 is a cross-sectional view, taken along line B-B in FIG. 7, of theablation electrode of the ablation system of FIG. 1.

FIG. 9 is an exemplary graph of force as a function of displacement of adeformable portion of the ablation electrode of the ablation system ofFIG. 1.

FIG. 10 is a perspective view of sensors and the ablation electrode ofthe ablation system of FIG. 1, with the sensors shown mounted to theablation electrode.

FIG. 11 is a perspective view of a sensor of the ablation system of FIG.1.

FIGS. 12A-12C are schematic representations of a method of forming theablation electrode of the ablation system of FIG. 1.

FIGS. 13A-13E are schematic representations of a method of inserting thecatheter of FIG. 2 into a patient.

FIGS. 14A-C are schematic representations of a method of positioning theablation electrode of the ablation system of FIG. 1 at a treatment siteof a patient.

FIGS. 15A-B are schematic representations of a method of irrigating theablation electrode of the ablation system of FIG. 1.

FIG. 16 is a schematic representation of a side view of a helicalirrigation element of a catheter of an ablation system.

FIG. 17 is a side view of an irrigation element of a catheter of anablation system, the irrigation element including a porous membrane.

FIG. 18 is a perspective view of a distal end portion of a catheter ofan ablation system.

FIG. 19 is a cross-sectional perspective view along cross-section C-C ofFIG. 18.

FIG. 20 is a perspective view of a distal end portion of a catheter ofan ablation system.

FIG. 21 is a cross-sectional perspective view along cross-section D-D ofFIG. 20.

FIG. 22 is a perspective view of a distal end portion of a catheter ofan ablation system.

FIG. 23 is a cross-sectional side view of the catheter of FIG. 22 alongcross-section E-E.

of FIG. 22.

FIG. 24 is a schematic representation of a trajectory around an outersurface of an ablation electrode of the catheter of FIG. 22, thetrajectory used to present simulation results of current densityassociated with the ablation electrode.

FIG. 25 is a graph of percentage change in simulated current densityalong the trajectory shown in FIG. 24, at a fixed distance of 1 mm froman outer surface of the ablation electrode.

FIG. 26 is a graph of depth and width of lesions applied to chickenbreast meat using the ablation electrode of FIG. 22 in axial and lateralorientations relative to the chicken breast meat.

FIG. 27 is a graph of RF energy as a function of time for a pulsed RFenergy profile having a first energy phase greater than a second energyphase.

FIG. 28 is a schematic representation of a lesion formed in tissuereceiving non-pulsed RF energy.

FIGS. 29A-B are schematic representations of heat transfer in tissue asthe pulsed RF energy profile of FIG. 27 is applied to tissue.

FIG. 30 is a flowchart of an exemplary process of pulsing RF energy toablate target tissue.

Like reference symbols in the various drawings indicate like elements.

DETAILED DESCRIPTION

The present disclosure is generally directed to systems and methods ofablating tissue of a patient during a medical procedure being performedon an anatomic structure of the patient. By way of non-limiting exampleand for the sake of clarity of explanation, the systems and methods ofthe present disclosure are described with respect to ablation of tissuein a heart cavity of the patient as part of an ablation treatmentassociated with the treatment of cardiac arrhythmia. However, it shouldbe appreciated that, unless otherwise specified, the systems and methodsof the present disclosure can be used for any of various differentmedical procedures, such as procedures performed on a hollow anatomicstructure of a patient, in which ablation of tissue is part of a medicaltreatment.

As used herein, the term “physician” should be considered to include anytype of medical personnel who may be performing or assisting a medicalprocedure.

FIG. 1 is a schematic representation of an ablation system 100 during acardiac ablation treatment being performed on a patient 102. Theablation system 100 includes a catheter 104 connected, via an extensioncable 106, to a catheter interface unit 108. The catheter interface unit108 can be a computing device that includes a processing unit 109 a, anon-transitory, computer readable storage medium 109 b, and a graphicaluser interface 110. The processing unit 109 a can be a controllerincluding one or more processors, and the storage medium 109 b can havestored thereon computer executable instructions for causing the one ormore processors of the processing unit 109 a to carry out one or moreportions of the various methods described herein, unless otherwiseindicated or made clear from the context.

A mapping system 112, a recording system 111, an irrigation pump 114,and a generator 116 can be connected to the catheter interface unit 108.The irrigation pump 114 can be removably and fluidly connected to theablation catheter 104 via fluid line 115. The generator 116 can also, orinstead, be connected, via one or more wires 117, to one or more returnelectrodes 118 attached to the skin of the patient 102. The recordingsystem 111 can be used throughout the ablation treatment, as well asbefore or after the treatment. The mapping system 112 can be used priorto and/or during an ablation treatment to map the cardiac tissue of thepatient 102 and determine which region or regions of the cardiac tissuerequire ablation.

Referring now to FIGS. 2-4, the catheter 104 can include a handle 120, acatheter shaft 122, an ablation electrode 124, sensors 126, and anirrigation element 128. The handle 120 is coupled to a proximal endportion 130 of the catheter shaft 122, and a distal end portion 132 ofthe catheter shaft 122 can be coupled to the irrigation element 128 andto the ablation electrode 124, which supports the sensors 126 in someimplementations. The handle 120 can, further or instead, be coupled tothe fluid line 115 and to one or more of the wires 117 for delivery ofirrigation fluid and electrical energy, respectively, along the cathetershaft 122, to the ablation electrode 124.

As described in further detail below, in a deployed state of theablation electrode 124, irrigation fluid exits irrigation holes 134defined by the irrigation element 128 and is directed toward an innerportion 136 of the ablation electrode 124 while an outer portion 138(opposite the inner portion 136) of the ablation electrode 124 is incontact with tissue as part of an ablation treatment. Spacing betweenthe irrigation holes 134 and the inner portion 136 of the ablationelectrode 124 can facilitate heat transfer between the irrigation fluidand the ablation electrode 124. For example, in the spacing between theirrigation holes 134 and the inner portion 136 of the ablation electrode124, the respective jets of irrigation fluid can develop turbulentcharacteristics. Without wishing to be bound by theory, it is believedthat, as compared to non-turbulent or less turbulent flow of irrigationfluid, increased turbulence can improve local heat transfer from theablation electrode 124 (e.g., from the inner portion 136 of the ablationelectrode 124) to the irrigation fluid. Additionally, or alternatively,blood can flow through the spacing between the irrigation holes 134 andthe inner portion 136 of the ablation electrode 124. As compared toconfigurations in which the flow of blood away from the treatment siteis impeded, the flow of blood through the spacing between the irrigationholes 134 and the inner portion 136 of the ablation electrode 124 can,additionally or alternatively, improve further the local heat transferfrom the outer portion 138 of the ablation electrode 124. In general, itshould be appreciated that such improved local heat transfer can reducethe likelihood of blood clot or charring.

As also described in further detail below, the ablation electrode 124can include a coupling portion 140 and a deformable portion 142. As usedherein, the terms “expandable” and “deformable” are usedinterchangeably, unless otherwise specified or made clear from thecontext. Thus, for example, it should be understood that the deformableportion 142 is expandable unless otherwise specified.

The coupling portion 140 is secured to the distal end portion 132 of thecatheter shaft 122, and the deformable portion 142 can extend distallyfrom the coupling portion 140. The deformable portion 142 of theablation electrode 142 can be deformed for delivery (e.g., through anintroducer sheath, such as an 8F introducer sheath) and expanded at atreatment site to have a cross-sectional dimension larger than across-sectional dimension of the catheter shaft 122. As compared tosmaller ablation electrodes, the ablation electrode 124 can providewider lesions within a shorter period of time, facilitating the creationof a pattern of overlapping lesions (e.g., reducing the likelihood ofarrythmogenic gaps, and reducing the time and number of lesions requiredfor an overlapping pattern, or both). Additionally, or alternatively, alarger tip can facilitate the delivery of more power for providing widerand deeper lesions.

Further, in an expanded state, the deformable portion 142 of theablation electrode 124 is deformable upon sufficient contact force withtissue, and the shape and extent of the deformation can be detectedbased, at least in part, upon signals received from the sensors 126 onthe deformable portion 142 of the ablation electrode 124. As describedin greater detail below, the sensors 126 can be used in one or moremodes of parameter measurement and, for example, can include one or moreof an electrode, a thermistor, an ultrasound transducer, and an opticalfiber. Additionally, or alternatively, the deformable portion 142 can beradiopaque such that deformation of the deformable portion 142 as aresult of contact with tissue is observable, for example, through X-rayor similar visualization techniques. The detection and/or observation ofthe deformation of the deformable portion 142 of the ablation electrode124 can, for example, provide improved certainty that an intendedtreatment is, in fact, being provided to tissue. It should beappreciated that improved certainty of positioning of an ablationelectrode with respect to tissue can reduce the likelihood of gaps in alesion pattern and, also or instead, can reduce the time and number ofablations otherwise required to avoid gaps in a lesion pattern.

The handle 120 can include a housing 145 and an actuation portion 146.In use, the actuation portion 146 can be operated to deflect the distalend portion 132 of the catheter shaft 122 to facilitate positioning theablation electrode 124 into contact with tissue at a treatment site. Thehandle 120 can include a fluid line connector 148 (e.g., a luerconnector) and an electrical connector 149. The fluid line 115 can beconnectable to the fluid line connector 148 and, in use, irrigationfluid (e.g., saline) can be delivered from the irrigation pump 114 tothe catheter 104 where, as described in further detail below, theirrigation fluid is ultimately deliverable through the irrigation holes134 of the irrigation element 128 to the inner portion 136 of theablation electrode 124. The extension cable 106 is connectable to theelectrical connector 149. In use, electrical energy can be deliveredfrom the ablation generator 116 to the catheter 104 where, as describedin further detail below, the electrical energy is ultimately deliverableto the ablation electrode 124 to ablate tissue in contact with the outerportion 138 of the ablation electrode 124.

The handle 120 can be attached to the proximal end portion 130 of thecatheter shaft 122 through any of various techniques, including one ormore of adhesive bonds, thermal bonds, and mechanical connections.

The catheter shaft 122 defines a lumen 151 extending from the proximalend portion 130 of the catheter shaft 122 to the distal end portion 132of the catheter shaft 122. The lumen 151 can be in fluid communicationwith the irrigation pump 114, via the fluid line 115 and the fluid lineconnector 148 of the handle 120, such that irrigation fluid can bepumped from the irrigation pump 114 to the irrigation holes 134 definedby the irrigation element 128. The catheter shaft 122 can also, orinstead, include electrical wires (such as any one or more of the wires117 shown in FIG. 1) extending along the catheter shaft 122 to carrysignals between the sensors 126 and the catheter interface unit 108 andthat carry electrical power from the ablation generator 116 to theablation electrode 124.

The catheter shaft 122 can be formed of any of various differentbiocompatible materials that provide the catheter shaft 122 withsufficient sturdiness and flexibility to allow the catheter shaft 122 tobe navigated through blood vessels of a patient. Examples of suitablematerials from which the catheter shaft 122 can be formed includepolyether block amides (e.g., Pebax®, available from Arkema of Colombes,France), nylon, polyurethane, Pellethane®, available from The LubrizolCorporation of Wickliffe, Ohio), and silicone. In certainimplementations, the catheter shaft 122 includes multiple differentmaterials along its length. The materials can, for example, be selectedto provide the catheter shaft 122 with increased flexibility at thedistal end, when compared to the proximal. The catheter shaft 122 canalso, or instead, include a tubular braided element that providestorsional stiffness while maintaining bending flexibility to one or moreregions of the catheter shaft 122. Further, or in the alternative, theshaft material can include radiopaque agents such as barium sulfate orbismuth, to facilitate fluoroscopic visualization.

The catheter shaft 122 can further include pull wires (not shown)mechanically coupled (e.g., via a ring secured to the catheter shaft122) to the distal end portion 132 of the catheter shaft 122 andmechanically coupled to the actuation portion 146 of the handle 120, asis well known in the art. During use, tension may be applied to thewires to deflect the distal end portion 132 of the catheter shaft 122 tosteer the catheter shaft 122 toward a treatment site.

The irrigation element 128 can include a stem 154 and a bulb 156. Thestem 154 can be coupled to the distal end portion 132 of the cathetershaft 122 in fluid communication with the lumen 151 of the cathetershaft 122 and, ultimately, with the irrigation pump 114. The bulb 156defines the irrigation holes 134 and is in fluid communication with thestem 154. Accordingly, irrigation fluid can pass through the lumen 151,through the stem 154, and can exit the irrigation element 128 throughthe irrigation holes 134 defined by the bulb 156.

The stem 154 can be substantially rigid and extend from the distal endportion 132 of the catheter shaft 122 in a direction having a distalcomponent and/or a radial component. For example, a radial extent of thestem 154 can direct irrigation fluid from an off-center position of thelumen 151 to a position along a center axis defined by the cathetershaft 122. Additionally, or alternatively, a distal extent of the stem154 can facilitate clearance of the catheter shaft 122 such that aportion of the irrigation holes 134 directed in the proximal directionhave a substantially unobstructed path to a portion of the inner portion136 of the ablation electrode 124 that is proximal to the irrigationelement 128. Thus, more generally, it should be understood that the sizeand shape of one or more of the stem 154, the bulb 156, and theirrigation holes 134 can be varied to achieve desired directionality ofthe irrigation fluid toward the inner portion 136 of the ablationelectrode 124.

The bulb 156 can be substantially rigid and, in certain implementations,formed of the same material as the stem 154. Additionally, oralternatively, the bulb 156 can be substantially spherical to facilitatedirecting irrigation fluid toward substantially the entire inner portion136 of the ablation electrode 124. It should be appreciated, however,that the bulb 156 can be any of various different shapes that facilitatemulti-directional dispersion of irrigation fluid toward the innerportion 136 of the ablation electrode 124.

In certain implementations, the irrigation holes 134 can be spacedcircumferentially and axially along the irrigation element. For example,the irrigation holes 134 can be spatially distributed along the bulb 156with at least a portion of the irrigation holes 134 arranged to directirrigation fluid in a distal direction with respect to the ablationelectrode 124 and at least a portion of the irrigation holes 134arranged to direct irrigation fluid in a proximal direction with respectto the ablation electrode 124. More generally, the irrigation holes 134can be distributed to produce a relatively uniform dispersion ofirrigation fluid along the inner portion 136 of the ablation electrode124 enveloping the irrigation element 128.

The overall radial extent of the irrigation element 128 can be less thanthe outer diameter of the catheter shaft 122. For example, theirrigation element 128 can remain in the same orientation in a deliveryconfiguration of the catheter 104 to the treatment and during treatmentat the treatment site while, as described in further detail below, theablation electrode 124 expands from a compressed state during deliveryto an expanded state during treatment at the treatment site. As alsodescribed in further detail below, the fixed orientation of theirrigation element 128 can facilitate using the irrigation element 128to act as a sensor or to carry a sensor. For example, a sensor can beadded to the irrigation element 128 to act as a sensor, in cooperationwith the sensors 126 such that the sensor on the irrigation element 128can act as a center electrode and the sensors 126 can act as surfaceelectrodes, as described in greater detail below.

While the irrigation element 128 can extend distal to the catheter shaft122, distal extent of the irrigation element 128 can be limited by theinner portion 136 of the ablation electrode 124. For example, theirrigation element 128 can be spaced proximal to the inner portion 136of the ablation electrode 124 such that the irrigation holes 134 directirrigation fluid toward the inner portion 136 of the ablation electrode124 in an expanded state. In particular, given that the deformableportion 142 of the ablation electrode 124 is intended to contact tissueduring ablation, the irrigation holes 134 can be oriented toward thedeformable portion 142 of the ablation electrode 124 to direct fluidtoward the inner portion 136 of the ablation electrode 124 along thedeformable portion 142 in contact with the tissue. Directing theirrigation fluid toward the deformable portion 142 of the ablationelectrode 124 in this way can, for example, reduce the likelihood ofunintended tissue damage resulting from the ablation treatment.

Referring now to FIG. 5, a schematic representation of a jet 158 ofirrigation fluid exiting one of the irrigation holes 134 and movingtoward the inner portion 136 of the ablation electrode 124 is shown justprior to impact between the jet 158 and the inner portion 136. Adistance “L” is a perpendicular distance between the irrigation hole 134and the inner portion 136 of the ablation electrode 124 when theablation electrode 124 is in an undeformed state (e.g., in the absenceof an external force applied to the ablation electrode 124). For thesake of clarity, a two-dimensional cross-section of a single jet isshown. However, it should be understood that, in use, a respectivethree-dimensional jet issues from each of the irrigation holes 134 andthe plurality of jets may interact with one another and/or with thepatient's blood, along the distance “L,” to create additional turbulenceat the inner portion 136 of the ablation electrode 124.

In implementations in which the irrigation holes 134 have a circularcross-section, the ratio of a diameter “D” of each of the irrigationholes 134 to the respective distance “L” between the respectiveirrigation hole 134 and the inner portion 136 of the ablation electrode124 can be greater than about 0.02 and less than about 0.2 (e.g.,greater than about 0.03 and less than about 0.06). Given other designconsiderations (e.g., manufacturability of hole sizes of the irrigationholes 134, acceptable pressure drop in the system, the influence ofblood flow between the irrigation element 128 and the ablation electrode124, or a combination thereof), this range of ratios will result inturbulent flow of irrigation fluid at the inner portion 136 of theablation electrode 124. Without wishing to be bound by theory, it isbelieved that, as compared to configurations with laminar flow and/orless turbulent flow of irrigation fluid past the inner portion 136 ofthe ablation electrode 124, the turbulent flow of irrigation fluidmoving from the irrigation holes 134 to the inner portion 136 of theablation electrode 124 results in increased heat transfer, which canreduce unintended tissue damage during ablation.

The size and number of the irrigation holes 134 defined by theirrigation element 128 are selected such that the pressure of irrigationfluid in the irrigation element 128 is sufficient to prevent blood fromentering the irrigation holes 134. For example, providing for somemargin of variation in pressure of the irrigation fluid, the size andnumber of the irrigation holes 134 defined by the irrigation element 128can be selected such that the pressure of the irrigation fluid in theirrigation element 128 is at least about 0.5 psi greater than thepressure of the blood of the patient 102. Further, in implementations inwhich the irrigation element 128 is expandable (e.g., a balloon), thepositive pressure difference between the irrigation fluid within theirrigation element 128 and the blood of the patient 102 can allow theirrigation element 128 to maintain an expanded shape. The size andnumber of the irrigation holes 134 can be, additionally oralternatively, selected to provide substantially uniform coverage of theirrigation fluid on the deformable portion 142 of the ablation electrode124.

In certain implementations, the irrigation holes 134 defined by theirrigation element 128 have a total open area of greater than about 0.05mm² and less than about 0.5 mm². In implementations in which theirrigation element 128 is substantially rigid (e.g., formed of stainlesssteel and/or platinum iridium), the irrigation holes 134 can be drilledinto the irrigation element 128. In implementations in which theirrigation element 127 is formed of an elastomer, the irrigation holes134 can be formed through the use of a laser.

Referring now to FIGS. 1-11, the ablation electrode 124 is a continuousstructure that acts as one electrode in the monopolar electrodeconfiguration of the ablation system 100, shown in FIG. 1. It should beappreciated, however, that the ablation electrode 124 can includeelectrically isolated portions such that the ablation electrode 124includes two electrodes of a bipolar electrode configuration.

The ablation electrode 124 can have an outer diameter of greater thanabout 4 mm and less than about 16 mm (e.g., about 8 mm) and,additionally or alternatively, a thickness of greater than about 0.07 mmand less than about 0.25 mm (e.g., about 0.17 mm). In certainimplementations, the ablation electrode 124 can have greater than about50 percent open area and less than about 95 percent open area (e.g.,about 80 percent open area). As used herein, the percentage of open areaof the ablation electrode 124 should be understood to be the ratio ofthe area through which fluid can flow from the outer portion 138 of theablation electrode 124 to the surface area of a convex hull thatincludes the outer portion 138 of the ablation electrode 124 and thestructural elements defining the outer portion 138 of the ablationelectrode, with the ratio expressed as a percentage. It should beappreciated that the open area of the ablation electrode 124 canfacilitate the flow of irrigation fluid and blood through ablationelectrode 124 during treatment. As compared to ablation electrodes thatimpede the flow of blood, the open area of the ablation electrode 124can reduce the likelihood of local heating of blood at the treatmentsite as ablation energy is delivered to the tissue. It should beappreciated that the delivery of irrigation fluid to the inner portion136 of the ablation electrode 124 can augment the cooling that occursthrough the flow of only blood through the open area.

In general, it should be appreciated that the dimensions of the ablationelectrode 124, including the dimensions related to the diameter,thickness, and/or open area, can facilitate retraction of the ablationelectrode 124. That is, the force required to retract the ablationelectrode 124 into a sheath (e.g., at the end of a procedure) are suchthat the ablation electrode 124 can be retracted by a physician withoutrequiring assistance of a separate mechanism to provide a mechanicaladvantage. Further, or instead, the dimensions of the ablation electrode124 can facilitate adequate expansion of the electrode 124. For example,in instances in which the electrode 124 is formed of nitinol, theablation electrode 124 can be dimensioned such that, in the compressedstate (e.g., for delivery), strain in the ablation electrode 124 is lessthan about ten percent. As a more general example, the ablationelectrode 124 can be dimensioned such that the ablation electrode 124 iscompressible to a size suitable for delivery (e.g., through an 8 Frenchsheath) using a force that avoids, or at least limits, plasticdeformation of the material of the ablation electrode 124. It should beappreciated that avoiding, or at least limiting, plastic deformation inthis way can facilitate expansion of the ablation electrode 124 in apredictable manner (e.g., to a full extent) in the absence of an appliedforce.

The coupling portion 140 of the ablation electrode 124 can be directlyor indirectly mechanically coupled to the catheter shaft 122. Forexample, the coupling portion 140 can include struts 144 a directlycoupled to the catheter shaft 122 or coupled to a transition partcoupled to the catheter shaft 122. Each strut 144 a can include aportion extending parallel to the catheter shaft 122 with the couplingportion 140 coupled to the catheter shaft 122 along the portion of thestrut 144 a extending parallel to the catheter shaft 122. Alternatively,or in addition, the coupling portion 140 can include a complete ringdirectly or indirectly mechanically coupled to the catheter shaft 122.

The coupling portion 140 can be electrically coupled to the generator116 via one or more of the wires 117 (shown in FIG. 1) and/or otherconductive paths extending from the generator 116, along the length ofthe catheter shaft 122, and to the coupling portion 140. For example,the coupling portion 140 can be fitted into the distal end portion 132of the catheter shaft 122, connected to wires extending to the generator116, and potted within an adhesive in the distal end portion 132 of thecatheter shaft 122. In use, electrical energy provided at the generator116 can be delivered to the coupling portion 140 and, thus, to thedeformable portion 142 of the ablation electrode 124, where theelectrical energy can be delivered to tissue of the patient 102.

The deformable portion 142 of the ablation electrode 124 can includestruts 144 b mechanically coupled to one another at joints 141 a todefine collectively a plurality of cells 147 of the ablation electrode124. Additionally, or alternatively, the struts 144 b can bemechanically coupled to one another by a fastener 141 b. Accordingly,each end of the struts 144 b can be coupled to an end of another strut144 b, to the fastener 141 b, or a combination thereof to define thedeformable portion 142 of the ablation electrode 124. For example, thestruts 144 b along the deformable portion 142 of the ablation electrodecan be coupled to one another, to the fastener 141 b, or to acombination thereof to define a closed shape along the deformableportion 142. Also, or instead, at least some of the struts 144 b can becoupled to the struts 144 a to transition between the deformable portion142 and the coupling portion 140 of the ablation electrode 124. Incertain implementations, the struts 144 b can be coupled to the struts144 a such that the coupling portion 140 defines an open shape along thecoupling portion 140 to facilitate, for example, securing the struts 144a to the distal end portion 132 of the catheter shaft 122.

The catheter shaft 122 defines a center axis C_(L)-C_(L) extending fromthe proximal end portion 130 to the distal end portion 132 of thecatheter shaft 122. The cells 147 can have a generally axial orientationrelative to the center axis C_(L)-C_(L). For example, each of the cells147 can have a respective symmetry plane passing through a distal end ofthe cell 147, a proximal end of the cell 147, and the center axisC_(L)-C_(L). Such an orientation can advantageously preferentiallyexpand and contract the cells 147 relative to the center axisC_(L)-C_(L), which can facilitate compressing the deformable portion 142of the ablation electrode 124 to a size suitable for delivery to atreatment site.

The center axis C_(L)-C_(L) can, for example, extend through thefastener 141 b in the absence of an external force applied to theablation electrode. Such alignment of the fastener 141 b can facilitate,in certain instances, location of the distal end portion 142 of theablation electrode 124 (e.g., by locating the fastener 141 b at atreatment site).

The fastener 141 b can be formed of a first material (e.g., a polymer)and the struts 144 b can be formed of a second material (e.g., anitinol) different from the first material. It should be appreciatedthat the material of the fastener 141 b can be selected for acombination of strength and electrical properties suitable formaintaining the struts 144 b coupled to one another while achieving acurrent density distribution suitable for a particular application. Theclosed shape of the deformable portion 142 can, for example, facilitatethe delivery of substantially uniform current density through theablation electrode 124 in a manner that, as compared to an electrodewith an open shape, is less dependent on the orientation of the ablationelectrode 124 relative to tissue, as described in greater detail below.

In general, each cell 147 can be defined by at least three struts 144 b.Also, or instead, each strut 144 b can define a portion of at least twoof the cells 147. The inner portion 136 of the ablation electrode 124can be in fluid communication with the outer portion 138 of the ablationelectrode 124 through the plurality of cells 147 such that, in use,irrigation fluid, blood, or a combination thereof can move through theplurality of cells 147 to cool the ablation electrode 124 and tissue inthe vicinity of the ablation electrode 124.

At least some of the plurality of cells 147 can be flexible in the axialand lateral directions such that the open framework formed by theplurality of cells 147 along the deformable portion 142 of the ablationelectrode 124 is similarly flexible. For example, at least some of theplurality of cells can be substantially diamond-shaped in theuncompressed state of the deformable portion 142 of the ablationelectrode 124. As used herein, substantially diamond-shaped includesshapes including a first pair of joints substantially aligned along afirst axis and a second pair of joints substantially aligned along asecond axis, different from the first axis (e.g., perpendicular to thefirst axis).

The flexibility of the open framework formed by the plurality of cells147 along the deformable portion 142 of the ablation electrode 124 can,for example, advantageously resist movement of the deformable portion142 in contact with tissue during a medical procedure. That is, thedeformable portion 142 can deform upon contact with tissue and thedeformable portion 142 can engage the tissue through one or more of thecells 147 to resist lateral movement of the deformable portion 142relative to the tissue. That is, as compared to a closed surface incontact with tissue, the deformable portion 142 will resist unintendedmovement (e.g., sliding with respect to the tissue) with which it is incontact. It should be appreciated that such resistance to movement canfacilitate, for example, more accurate placement of lesions.

The struts 144 a, 144 b can have dimensions that differ fromcorresponding dimensions of other ones of the struts 144 a, 144 b. Forexample, the struts 144 b can have a dimension (e.g., width) thatdiffers from a corresponding dimension of another one of the struts 144b. Varying dimensions of the struts 144 a, 144 b, for example, fordelivery of substantially uniform current density through the deformableportion 142 of the ablation electrode 124, as described in greaterdetail below. Additionally, or alternatively, the struts 144 a can bewider than the struts 144 b to facilitate fixing the struts 144 adirectly or indirectly to the distal end portion 132 of the cathetershaft 122.

In general, the struts 144 b can be dimensioned and arranged relative toone another for delivery of substantially uniform current densitythrough the deformable portion 142 of the ablation electrode 124, asdescribed in greater detail below. By way of non-limiting example, afirst set of the struts 144 b can have a first width, and a second setof the struts 144 b can have a second width, different from the firstwidth. Continuing with this example, the first set of the struts 144 bcan be axially spaced relative to the second set of the struts 144 b.Such axial distribution of the material of the struts can be useful, forexample, for achieving a desired current density profile (e.g., asubstantially uniform current density profile). As another non-limitingexample, at least some of the struts 144 b can have a non-uniform widthalong a length of the respective strut 144 b such that the amount ofmaterial along a given strut is varied, resulting in an associateddistribution in current density. For example, at least some of thestruts 144 b can include a width increasing along the length of therespective strut 144 b in a direction from a proximal region to a distalregion of the ablation electrode 124.

In general, the plurality of cells 147 can be disposed circumferentiallyand axially about the ablation electrode 124. More specifically, asdescribed in greater detail below, the plurality of cells 147 can bearranged about the ablation electrode 124 (e.g., along the deformableportion 142 of the ablation electrode 124) to facilitate contraction andexpansion of the deformable portion 142 and/or to facilitatesubstantially uniform distribution of current density along thedeformable portion 142.

Each cell 147 can be bounded. In particular, as used herein, a boundedcell 147 includes a cell entirely defined by the struts 144 b, thejoints 141 a, sensors 126 disposed along the struts 144 b or the joints141 a, or a combination thereof. As described in further detail below,the struts 144 b can be connected to one another at the joints 141 a aspart of a unitary or substantially unitary structure. Additionally, oralternatively, as also described in greater detail below, the struts 144b can be connected to one another through welds, fasteners, or othermechanical connections at one or more of the joints 141 a.

The struts 144 b can be movable relative to one another through flexingat the joints 141 a. More specifically, the struts 144 b can be flexiblerelative to one another to move the deformable portion 142 between acompressed state, in the presence of an external force, and anuncompressed state, in the absence of the external force. For example, amaximum radial dimension (alternatively referred to herein as a lateraldimension) of the ablation electrode can increase by at least a factorof 2 as the coupled struts 144 b move relative to one another totransition the ablation electrode 124 from a compressed state, in thepresence of external force, to an uncompressed state, in the absence ofexternal force. This ratio of increase in size is achieved through theuse of the open framework of cells 147 formed by the struts 144 b, whichmakes use of less material than would otherwise be required for a solidshape of the same size. Further, or instead, it should be appreciatedthat the ratio of the increase in size achieved through the use of theopen framework of cells 147 is useful for delivery to a treatment sitethrough an 8 French sheath while also facilitating the formation oflarge lesions at the treatment site.

Through flexing at the joints 141 a and associated movement of thestruts 144 b, the deformable portion 142 can be resiliently flexible inan axial direction relative to the catheter shaft 122 and/or in a radialdirection relative to the catheter shaft 122. Additionally, oralternatively, the deformable portion 142 can be expandable (e.g.,self-expandable) from the compressed state to the uncompressed state.For example, the struts 144 b can be biased to move in one or moredirections away from one another to self-expand the deformable portion142 from the compressed state to the uncompressed state.

In the uncompressed state, the struts 144 b, the joints 141 a, and thecells 147 together can form an open framework having a conductivesurface along the deformable portion 142 of the ablation electrode 124.For example, the open framework formed by the struts 144 b, the joints141 a, and the cells 147 can have greater than about 50 percent openarea along the outer portion 138 of the ablation electrode 124 when thedeformable portion 142 of the ablation electrode 124 is in theuncompressed state. Continuing with this example, in the uncompressedstate, the combined open area of the cells 147 can be greater than thecombined area of the struts 144 b and the joints 141 a along the outerportion 138 of the ablation electrode 124. Further, or instead, at leastsome of the cells 147 can have a larger area in the uncompressed stateof the deformable portion 142 than in the compressed state of thedeformable portion 142.

More generally, the open area defined by the cells 147 can have amagnitude and spatial distribution sufficient to receive the struts 144b and, optionally the sensors 126, as the deformable portion 142collapses from the uncompressed state to the compressed state.Accordingly, it should be appreciated that the magnitude of the ratio ofthe combined open area of the cells 147 to the combined area of thestruts 144 b and the joints 141 a can, among other things, be useful forvarying the degree of expansion of a deformable portion 142 of theablation electrode 124 relative to a delivery state in which thedeformable portion 142 is in a compressed state. That is, the ratio ofthe combined open area of the cells 147 to the combined area of thestruts 144 b and the joints 141 a can facilitate minimally invasivedelivery (e.g., delivery through an 8 Fr sheath) of the ablationelectrode 124.

By way of example, a maximum radial dimension of the ablation electrode124 can increase by at least a factor of 2 as the struts 144 b moverelative to one another to transition the ablation electrode 124 (e.g.,the deformable portion 142 of the ablation electrode 124) from acompressed state, in the presence of an external force (e.g., a radialforce), to an uncompressed state, in the absence of an external force.Additionally, or alternatively, the struts 144 b can be movable relativeto one another such that a maximum radial dimension of the deformableportion 142, in the uncompressed state, is at least about 20 percentgreater than a maximum radial dimension of the catheter shaft 122 (e.g.,greater than a maximum radial dimension of the distal end portion 132 ofthe catheter shaft 122). It should be appreciated that the extension ofthe deformable portion 142 beyond the maximum radial dimension of thecatheter shaft 122 can facilitate creation of a lesion having a largewidth, as compared to an ablation electrode constrained by a radialdimension of a catheter shaft.

In certain implementations, the ablation electrode 124 has a maximumaxial dimension that changes by less than about 33 percent (e.g., about20 percent) as the struts 144 b expand (e.g., self-expand) from theuncompressed state to the compressed state upon removal of an externalradial force applied to the ablation electrode 124.

At least some of the struts 144 b extend in a direction having acircumferential dimensional component with respect to an axis defined bythe catheter shaft 122 (e.g., an axis defined by the proximal endportion 130 and the distal end portion 132 of the catheter shaft 122).That is, the struts 144 b extending in a direction having acircumferential dimensional component with respect to an axis defined bythe catheter shaft 122 are nonparallel to the axis defined by thecatheter shaft 122. In some implementations, at least some of the struts144 b include a non-uniform width along a length of the respective strut144 b. Because current density at a given point along the ablationelectrode 124 is a function of surface area at the given point along theablation electrode 124, the non-uniform width of a given one of thestruts 144 b can facilitate balancing current density to achieve atarget current density profile along the deformable portion 142 of theablation electrode 124. As described in greater detail below, thecircumferential extension and/or the non-uniform width along the lengthof at least some of the struts 144 b can facilitate substantiallyuniform distribution of current density along the deformable portion 142during a medical procedure.

While a large surface area of the struts 144 b can be advantageous forthe delivery of energy to tissue, an upper boundary of the area of thestruts 144 b can be the geometric configuration that will allow thestruts 144 b to collapse into the compressed state (e.g., duringdelivery to the treatment site and/or during contact with tissue at thetreatment site) without interfering with one another. Additionally, oralternatively, the struts 144 b can be twisted towards the inner portion136 of the ablation electrode 124. It should be appreciated that, ascompared to struts that are not twisted, the twisted struts 144 b can bewider while still being collapsible into the compressed state withoutinterfering with one another. Further in addition or further in thealternative, an upper boundary of the area of the struts 144 b can bethe amount of open area of the deformable portion 142 that willfacilitate appropriate heat transfer (e.g., during ablation) at theablation electrode 124 through the movement of irrigation fluid and/orblood through the deformable portion 142.

As used herein, the uncompressed state of the deformable portion 142refers to the state of the deformable portion 142 in the absence of asubstantial applied force (e.g., an applied force less than about 5grams). Thus, the uncompressed state of the deformable portion 142includes a state of the ablation electrode 124 in the absence ofexternal forces. Additionally, the uncompressed state of the deformableportion 142 includes a state of the ablation electrode 124 in which asmall applied force (e.g., less an about 5 grams) is present, but isinsufficient to create a significant deformation in the deformableportion 142.

In the uncompressed state of the deformable portion 142, the ablationelectrode 124 can be bulbous. For example, in the uncompressed state,the deformable portion 142 can be a shape having symmetry in a radialdirection and/or an axial direction relative to the catheter shaft 122.For example, in the uncompressed state the deformable portion 142 can bean ellipsoidal shape such as, for example, a substantially sphericalshape (e.g., an arrangement of the struts 144 b, each strut 144 b havinga planar shape, relative to one another to approximate a sphericalshape). Additionally, or alternatively, in the uncompressed state, thedeformable portion 142 can be a symmetric shape (e.g., a substantiallyellipsoidal shape or another similar shape contained between a firstradius and a perpendicular second radius, the first radius and thesecond radius within 30 percent of one another in magnitude). Symmetryof the deformable portion 142 can, for example, facilitate symmetricdelivery of ablation energy to the tissue in a number of orientations ofthe deformable portion 142 relative to the tissue being ablated.

At least when the deformable portion 142 is in the uncompressed state,the deformable portion 142 can envelop the irrigation element 128 suchthat the irrigation element 128 directs irrigation fluid toward theinner portion 136 of the ablation electrode 124. Accordingly, inimplementations in which the deformable portion 142 is symmetric, theirrigation element 128 can provide a substantially uniform distributionof irrigation fluid along the inner portion 136 of the ablationelectrode 124, as the deformable portion 142 in the uncompressed stateenvelops the irrigation element 128.

In certain implementations, the largest cross-sectional dimension of thedeformable portion 142 in the uncompressed state is larger than thelargest cross-sectional dimension of the catheter shaft 122. Thus,because the deformable portion 142 is expandable to extend beyond thecatheter shaft 122, the deformable portion 142 can create a lesion thatis larger than the largest dimension of the catheter shaft 122 such thatthe resulting lesions are wider and deeper than lesions created byablation electrodes that do not expand. For example, in the uncompressedstate, the deformable portion 142 can be substantially circular at thelargest cross-sectional dimension of the deformable portion, and thecatheter shaft 122 can be substantially circular at the largestcross-sectional dimension of the catheter shaft 122. Thus, continuingwith this example, the outer diameter of the deformable portion 142 islarger than the outer diameter of the catheter shaft 122 such that thesize of the ablation created by the ablation electrode 124 is largerthan the outer diameter of the catheter shaft 122.

The compressed state of the ablation electrode 124, as used herein,refers to the state of the ablation electrode in the presence of a force(e.g., a force of about 5 grams or greater) sufficient to cause thedeformable portion 142 to flex (e.g., through flexing of one or more ofthe joints 141 a) to a significant extent. Thus, for example, thecompressed state of the ablation electrode 124 includes the reduced sizeprofile of the ablation electrode 124 during introduction of thecatheter 104 to the treatment site, as described in further detailbelow. The compressed state of the ablation electrode 124 also includesone or more states of deformation and/or partial deformation resultingfrom an external force exerted along one or more portions of thedeformable portion 142 of the ablation electrode 124 as a result ofcontact between the deformable portion 142 and tissue at the treatmentsite.

The compressed state of the ablation electrode 124 can have apredetermined relationship with respect to an applied force. Forexample, the compressed state of the ablation electrode 124 can have asubstantially linear (e.g., within ±10 percent) relationship withapplied forces in the range of forces typically applied during anablation procedure (e.g., about 1 mm deformation in response to 60 gramsof force). It should be appreciated that such a predeterminedrelationship can be useful, for example, for determining the amount ofapplied force on the ablation electrode 124 based on a measured amountof deformation of the ablation electrode 124. That is, given thepredetermined relationship between deformation of the ablation electrode124 and an amount of an applied force, determining the amount ofdeformation of the ablation electrode 124 can provide an indication ofthe amount of force being applied by the ablation electrode 124 ontissue at the treatment site. As such, the determined amount ofdeformation of the ablation electrode 124 can be used, for example, asfeedback to control the amount of force applied to tissue at thetreatment site. Methods of determining the amount of deformation of theablation electrode 124 are described in greater detail below.

FIG. 9 is a graph of an exemplary relationship between force anddisplacement for different amounts of force applied to the deformableportion 142 of the ablation electrode 124. The deformable portion 142 ofthe ablation electrode 124 can have different force-displacementresponses, depending on the direction of the force applied to thedeformable portion 142 of the ablation electrode 124. For example, asshown in the exemplary relationship in FIG. 9, the deformable portion142 of the ablation electrode 124 can have an axial force-displacementresponse 143 a and a lateral force-displacement response 143 b. That is,the response of the deformable portion 142 to the application of forcecan depend on the direction of the applied force. In the specificexample of FIG. 9, the deformable portion 142 can be stiffer in theaxial direction than in the lateral direction.

In general, the axial force-displacement 143 a and the lateralforce-displacement response 143 b can be reproducible and, thus, theamount of force applied to the deformable portion 142 of the ablationelectrode 124 in the axial and/or lateral direction can be reliablydetermined based on respective displacement of the deformable portion142. Accordingly, as described in greater detail below, the determineddisplacement of the deformable portion 142 can be used to determine theamount and direction of force applied to the deformable portion 142.More generally, because the deformable portion 142 is movable between acompressed state and an uncompressed state in a reproducible manner inresponse to applied force, the deformable portion 142 of the ablationelectrode can be useful as a contact force sensor and, thus, canfacilitate application of appropriate force during ablation treatment.

In certain implementations, at least a portion of the ablation electrode124 is radiopaque, with the deformable portion 142 observable throughthe use of fluoroscopy or other similar visualization techniques. Forexample, the deformable portion 142 of the ablation electrode 124 can beradiopaque such that fluoroscopy can provide an indication of thedeformation and/or partial deformation of the deformable portion 142and, therefore, provide an indication of whether the deformable portion142 is in contact with tissue.

A material for forming the ablation electrode 124 can include nitinol,which is weakly radiopaque and is repeatably and reliably flexiblebetween a compressed state and an uncompressed state. Additionally, oralternatively, the material for forming the ablation electrode 124 canbe coated with one or more of gold or tantalum. Thus, continuing withthis example, the deformable portion 142 of the ablation electrode 124(e.g., the struts 144 b) can be formed of nitinol, either alone orcoated, such that ablation energy is delivered through the nitinolforming the deformable portion 142 for delivery to tissue to createlesions.

As described in further detail below, the deformation and/or partialdeformation of the deformable portion 142 in the compressed state can beadditionally, or alternatively, detected by the sensors 126 to providefeedback regarding the extent and direction of contact between thedeformable portion 142 of the ablation electrode 124 and the tissue atthe treatment site.

Referring now to FIGS. 10 and 11, the sensors 126 can be mounted alongthe deformable portion 142 of the ablation electrode 124. Each sensor126 can be electrically insulated from the ablation electrode 124 andmounted on one of the struts 144 b of the deformable portion 142. Forexample, each sensor 126 can be mounted to the deformable portion 142using a compliant adhesive (e.g., a room temperature vulcanized (RTV)silicone), any of various different mechanical retaining features (e.g.,tabs) between the sensor 126 and the ablation electrode 124, and/ormolding or overmolding of the sensor 126 to the ablation electrode 124.Because the struts 144 b do not undergo significant flexing as thedeformable portion 142 moves between the compressed state and theuncompressed state, mounting the sensors 126 on the struts 144 b canreduce physical strain on the sensors 126, as compared to mounting thesensors 126 on sections of the deformable portion 142 that experiencelarger amounts of flexing as the deformable portion 142 moves betweenthe compressed state and the uncompressed state.

In general, the sensors 126 can be positioned along one or both of theinner portion 136 and the outer portion 138 of the ablation electrode124. Wires 148 extend from each sensor 126, along the inner portion 136of the ablation electrode 124, and into the catheter shaft 122 (FIG. 2).The wires 148 are in electrical communication with the catheterinterface unit 108 (FIG. 1) such that, as described in further detailbelow, each sensor 126 can send electrical signals to and receiveelectrical signals from the catheter interface unit 108 during use.

The sensors 126 can be substantially uniformly spaced from one another(e.g., in a circumferential direction and/or in an axial direction)along the deformable portion 142 of the ablation electrode 124 when thedeformable portion 142 of the ablation electrode 124 is in anuncompressed state. Such substantially uniform distribution of thesensors 126 can, for example, facilitate determining an accuratedeformation and/or temperature profile of the deformable portion 142during use.

Each sensor 126 can act as an electrode to detect electrical activity ofthe heart in an area local to the sensor 126 and, further or instead,each sensor 126 can include a flexible printed circuit 150, a thermistor152 secured between portions of the flexible printed circuit 150, and atermination pad 155 opposite the thermistor 152. As an example, thesensor 126 can be mounted on the deformable portion 142 of the ablationelectrode 124 with the thermistor 152 disposed along the outer portion138 of the deformable portion 142 and the termination pad 154 disposedalong the inner portion 136 of the deformable portion 142. In certaininstances, the thermistor 152 can be disposed along the outer portion138 to provide an accurate indication of tissue temperature. A thermallyconductive adhesive or other conductive material can be disposed overthe thermistor 152 to secure the thermistor 152 to the flexible printedcircuit 150.

In some implementations, each sensor 126 can include a radiopaqueportion and/or a radiopaque marker. The addition of radiopacity to thesensor 126 can, for example, facilitate visualization (e.g., usingfluoroscopy) of the sensor 126 during use. Examples of radiopaquematerial that can be added to the sensor 126 include: platinum, platinumiridium, gold, radiopaque ink, and combinations thereof. The radiopaquematerial can be added in any pattern that may facilitate visualizationof the radiopaque material such as, for example, a dot and/or a ring.

In use, each sensor 126 can, further or instead, act as an electrode todetect electrical activity in an area of the heart local to therespective sensor 126, with the detected electrical activity forming abasis for an electrogram associated with the respective sensor 126 and,further or instead, can provide lesion feedback. The sensors 126 can bearranged such that electrical activity detected by each sensor 126 canform the basis of unipolar electrograms and/or bipolar electrograms.Additionally, or alternatively, the sensors 126 can cooperate with acenter electrode (e.g., an electrode associated with an irrigationelement, such as a center electrode 235 in FIG. 22, or the irrigationelement itself, such as the irrigation element 128 in FIG. 3) to providenear-unipolar electrograms, as described in greater detail below. Itshould be appreciated that the sensors 126 and a center electrode cancooperate to provide near-unipolar electrograms in addition, or as analternative, to any one or more of the various different methods ofdetermining contact, shape, force, and impedance described herein, eachof which may include further or alternative cooperation between thesensors 126 and a center electrode.

FIGS. 12A-12C are a schematic representation of an exemplary method ofmaking the ablation electrode 124 from a sheet 156 of material.

As shown in FIG. 12A, the sheet 156 of material is flat. As used herein,a flat material includes a material exhibiting flatness within normalmanufacturing tolerances associated with the material. The material ofthe sheet 156 is conductive and, optionally, also radiopaque. Forexample, the sheet 156 can be nitinol.

The thickness of the sheet 156 can correspond to the thickness of theablation electrode 124. For example, the thickness of the sheet 156 canbe greater than about 0.1 mm and less than about 0.20 mm. In certainimplementations, however, the thickness of the sheet 156 can be largerthan at least a portion of the thickness of the ablation electrode 124such that the removal of material from the flat sheet includes removalof material in a thickness direction of the sheet 156. For example,material can be selectively removed in the thickness direction of thesheet 156 to produce the ablation electrode 124 with a variablethickness (e.g., the ablation electrode 124 can be thinner along thejoints 141 a (FIGS. 6-8) to facilitate flexing).

As shown in FIG. 12B, material can be removed from the sheet 156 todefine the open area of the deformable portion 142 and to define thecoupling portion 140. In particular, the removal of material along thedeformable portion 142 can define the struts 144 b and the joints 141 a.

The material of the sheet 156 can be removed, for example, by using anyof various different subtractive manufacturing processes. As an example,the material of the sheet 156 can be removed using chemical etching(also known as photo etching or photochemical etching) according to anyone or more methods that are well known in the art and generally includeremoving material by selectively exposing the material to an acid toremove the material. Additionally, or alternatively, the material of thesheet 156 can be removed by laser cutting the material. The removal ofmaterial can be done to create openings in the sheet 156 and/or to thinselected portions of the sheet 156.

Because the sheet 156 is flat, removing material from the sheet 156 toform the deformable portion 142 can have certain advantages. Forexample, as compared to removing material from a curved workpiece,removing material from the sheet 156 can facilitate controllinggeometric tolerances. Additionally, or alternatively, as compared toremoving material from a curved workpiece, removing material from thesheet 156 can facilitate placement of sensors (e.g., while the sheet 156is flat). In certain implementations, as compared to removing materialfrom a curved workpiece, removing material from the sheet 156 canreduce, or even eliminate, the need to shape set the sheet 156, as thedistal and proximal sections can be put together to form the shape ofthe ablation electrode 124 (e.g., a substantially spherical shape).

In certain implementations, the material removed from the sheet 156 candefine eyelets 157 disposed at one end of at least a portion of thestruts 144 b. The eyelets 157 can be, for example, defined at theintersection of two or more of the struts 144 b.

In general, the material forming the ablation electrode 124 can beprocessed at any of various different stages of fabrication of theablation electrode 124. For example, with the material removed from thesheet to define the struts 144 a, 144 b and the joints 141 a as shown inFIG. 12B, one or more surfaces of the material can be electropolished.Such electropolishing can, for example, be useful for smoothing surfacesand/or otherwise producing fine adjustments in the amount of materialalong the ablation electrode 124.

As shown in FIG. 12C, with the material removed from the sheet 156 todefine the struts 144 a, 144 b and the joints 141 a, the sections 158are bent into proximity with one another and joined to one another toform a unitary three-dimensional structure having the overall shape ofthe ablation electrode 124. For example, the struts 144 b can be benttoward one another and the fastener 141 b can couple the portion of thestruts 144 b to one another at the eyelets 157, thus defining a closeddistal end of the deformable portion 142 of the ablation electrode 124.With the deformable portion 142 defined, the fastener 141 b can be at adistalmost portion of the deformable portion 142.

In certain implementations, the fastener 141 b can be a rivet. In suchimplementations, the eyelets 157 can be, for example, aligned with oneanother such that the fastener 141 b passes through the aligned eyelets157 to hold them together through force exerted on the eyelets 157 bythe fastener 141 b. Additionally, or alternatively, a secondaryoperation such as welding can secure the fastener 141 b to the struts144 b at the eyelets 157.

Referring now to FIGS. 13A-E, to perform a cardiac ablation treatment,the distal end portion 132 of the catheter shaft 122 and, thus, theablation electrode 124 can be first introduced into the patient,typically via a femoral vein or artery. FIGS. 13A-E schematicallyillustrate a series of steps carried out to introduce the ablationelectrode 124 into the patient.

In a first step, shown in FIG. 13A, an introducer sheath 162 ispositioned within a blood vessel of the patient (e.g., the femoralartery of the patient) and the ablation electrode 124 is positioned forinsertion into the introducer sheath 162.

In a second step, shown in FIG. 13B, the user grasps the handle 120 ofthe catheter 104 and distally advances an insertion sheath 164 along thecatheter shaft 122 until the insertion sheath 164 surrounds the ablationelectrode 124. As the insertion sheath 164 is advanced over the ablationelectrode 124, the ablation electrode 124 collapses to a diametercapable of being inserted into the introducer sheath 162.

In a third step, shown in FIG. 13C, the user inserts the insertionsheath 164 (containing the ablation electrode 124) into the introducersheath 162 and distally advances the catheter 104.

In a fourth step, shown in FIG. 13D, after positioning the ablationelectrode 124 within the introducer sheath 162, the ablation electrode124 is advanced out of the insertion sheath 164 that is then leftsurrounding the proximal end portion 130 of the catheter shaft 122throughout the remainder of the treatment.

In a fifth step, shown in FIG. 13E, the catheter 104 is advanced throughthe introducer sheath 162 and the patient's vasculature until theablation electrode 124 reaches the treatment site in the heart of thepatient. As the ablation electrode 124 is extended distally beyond theintroducer sheath 162, the ablation electrode 124 can expand to theuncompressed state.

Because the ablation electrode 124 is collapsible, the introducer sheath162 can have a small diameter that can be inserted through acorrespondingly small insertion site. In general, small insertion sitesare desirable for reducing the likelihood of infection and/or reducingthe amount of time required for healing. In certain implementations, theintroducer sheath 162 can have an 8 French diameter, and the deformableportion 142 (FIG. 3) of the ablation electrode 124 can be collapsible toa size deliverable through the introducer sheath 162 of this size. Insome implementations, the irrigation element 128 is additionallycollapsible to a size smaller than the size of the ablation electrode124 such that the irrigation element 128 and the ablation electrode 124are, together, deliverable through the introducer sheath 162 of thissize.

FIGS. 14A-C schematically represent an exemplary method of positioningthe deformable portion 142 of the ablation electrode 124 into contactwith tissue “T” at the treatment site. It should be appreciated that,because the delivery of ablation energy to the tissue “T” at thetreatment site is enhanced by contact between the ablation electrode 124and the tissue “T,” such contact is established prior to delivery ofablation energy.

In a first step, shown in FIG. 14A, the deformable portion 142 of theablation electrode 124 is away from the tissue “T” and, thus, in anuncompressed state. In certain instances, this uncompressed state isobservable through fluoroscopy. That is, the shape of the deformableportion 142 can be observed in the uncompressed state.

In a second step, shown in FIG. 14B, the deformable portion 142 of theablation electrode 124 makes initial contact with the tissue “T.”Depending on the nature of the contact between the tissue “T” and thedeformable portion 142 of the ablation electrode 124, deformation of thedeformable portion 142 may or may not be observable through fluoroscopyalone. For example, the contact force on the deformable portion 142 maybe insufficient to compress the deformable portion 142 to an extentobservable using fluoroscopy. Additionally, or alternatively, thecontact may not be observable, or may be difficult to observe, in thedirection of observation provided by fluoroscopy.

In a third step, shown in FIG. 14C, the deformable portion 142 of theablation electrode 124 is moved further into contact with the tissue “T”such that sufficient contact is established between the deformableportion 142 and the tissue “T” to deform the deformable portion 142.While such deformation may be observable using fluoroscopy, the degreeand/or direction of the deformation is not readily determined usingfluoroscopy alone. Further, as is also the case with initial contact,the contact and/or degree of contact may not be observable, or may bedifficult to observe, in the direction of observation provided byfluoroscopy. Accordingly, as described in greater detail below,determining apposition of the deformable portion 142 to the tissue “T”can, additionally or alternatively, include sensing the position of thedeformable portion 142 based on signals received from the sensors 126.

Referring again to FIGS. 1 and 3, the sensors 126 can be used todetermine the shape of the deformable portion 142 of the ablationelectrode 124 and, thus, determine whether and to what extent certainregions of the deformable portion 142 are in contact with the tissue“T.” It should be appreciated, however, that the sensing methodsdescribed herein can be carried out using the sensors 126, alone or incombination with another electrode, such as an electrode carried on anirrigation element, as described in greater detail below.

For example, the processing unit 109 a can control the generator 116and/or another electrical power source to drive an electrical signalbetween any number and combination of electrode pairs formed by anycombination of electrodes associated with the ablation electrode 124,and the processing unit 109 can receive a signal (e.g., a signalindicative of voltage) from another electrode pair or the same electrodepair. For example, the processing unit 109 a can control the generator116 to drive one or more of the sensors 126, the ablation electrode 124,the irrigation element 128, and a center electrode (e.g., a centerelectrode 235 shown in FIG. 22). Additionally, or alternatively,multiple pairs can be driven in a multiplexed manner using timedivision, frequency division, code division, or combinations thereof.The processing unit 109 a can also, or instead, receive one or moremeasured electrical signals from one or more of the sensors 126, theablation electrode 124, the irrigation element 128, and a centerelectrode (e.g., the center electrode 235 shown in FIG. 22). The drivenelectrical signal can be any of various, different forms, including, forexample, a prescribed current or a prescribed voltage. In certainimplementations, the driven electrical signal is an 8 kHz alternatingcurrent applied between one of the sensors 126 and the irrigationelement 128.

In an exemplary method, the impedance detected by an electrode pair canbe detected (e.g., as a signal received by the processing unit 109 a)when an electrical signal is driven through the electrode pair. Theimpedance detected for various electrode pairs can be compared to oneanother and relative distances between the members of each electrodepair determined. For example, if the sensors 126 are identical, eachsensor 126 can be driven as part of a respective electrode pairincluding the irrigation element 128. For each such electrode pair, themeasured impedance between the electrode pair can be indicative ofrelative distance between the particular sensor 126 and the irrigationelement 128 forming the respective electrode pair. In implementations inwhich the irrigation element 128 is stationary while electrical signalsare driven through the electrode pairs, the relative distance betweeneach sensor 126 and the irrigation element 128 can be further indicativeof relative distance between each sensor 126 and each of the othersensors 126. In general, driven electrode pairs with lower measuredimpedance are closer to one another than those driven electrode pairswith higher measured impedance. In certain instances, electrodesassociated with the ablation electrode 124 (e.g., one or more of thesensors 126) that are not being driven can be measured to determineadditional information regarding the position of the driven currentpair.

The current measurements received by the processing unit 109 a andassociated with the driven current pairs alone, or in combination withthe current measurements at the sensors 126 that are not being driven,can be fit to a model and/or compared to a look-up table to determinedisplacement of the deformable portion 142 of the ablation electrode124. For example, the determined displacement of the deformable portion142 of the ablation electrode 124 can include displacement in at leastone of an axial direction or a lateral (radial) direction. It should beappreciated that, because of the spatial separation of the current pairsin three dimensions, the determined displacement of the deformableportion 142 of the ablation electrode 124 can be in more than onedirection (e.g., an axial direction, a lateral direction, andcombinations thereof). Additionally, or alternatively, the determineddisplacement of the deformable portion 142 of the ablation electrode 124can correspond to a three-dimensional shape of the deformable portion142 of the ablation electrode 124.

Based on the determined displacement of the deformable portion 142 ofthe ablation electrode 124, the processing unit 109 a can send anindication of the shape of the deformable portion 142 of the ablationelectrode 124 to the graphical user interface 110. Such an indication ofthe shape of the deformable portion 142 can include, for example, agraphical representation of the shape of the deformable portion 142corresponding to the determined deformation.

In implementations in which the force-displacement response of thedeformable portion 142 is reproducible (e.g., as shown in FIG. 9), theprocessing unit 109 a can determine force applied to the deformableportion 142 based on the determined displacement of the deformableportion 142. For example, using a lookup table, a curve fit, or otherpredetermined relationship, the processing unit 109 a can determine thedirection and magnitude of force applied to the deformable portion 142based on the magnitude and direction of the displacement of thedeformable portion 142, as determined according to any one or more ofthe methods of determining displacement described herein. It should beappreciated, therefore, that the reproducible relationship between forceand displacement along the deformable portion 142, coupled with theability to determine displacement using the sensors 126 disposed alongthe deformable portion 142, can facilitate determining whether anappropriate amount of force is being applied during an ablationtreatment and, additionally or alternatively, can facilitate determiningappropriate energy and cooling dosing for lesion formation.

FIGS. 15A-B schematically represent an exemplary method of cooling theablation electrode 124 at the treatment site with irrigation fluid fromthe irrigation element 128. For the sake of clarity of illustration, asingle jet of irrigation fluid is shown. It should be appreciated,however, that a plurality of jets issue from the irrigation element 128during use. In certain implementations, the irrigation fluid issubstantially uniformly directed to the inner portion 136 of theablation electrode 124. Additionally, or alternatively, a portion of theirrigation fluid can be directed in a direction distal to the irrigationelement 128 and a portion of the irrigation fluid can be directed in adirection proximal to the irrigation element 128.

In a first step, shown in FIG. 15A, the ablation electrode 124 ispositioned at the treatment site with the outer portion 138 disposedtoward tissue. A baseline flow of irrigation fluid is delivered to theirrigation element 128 prior to delivery of ablation energy to theablation electrode 124. The baseline flow of irrigation fluid can be,for example, about 0.5 psi above the patient's blood pressure to reducethe likelihood that blood will enter the irrigation element 128 andclot. Further, as compared to always delivering irrigation fluid at ahigher pressure, the delivery of this lower pressure of irrigation fluidwhen ablation energy is not being delivered to the ablation electrode124 can reduce the amount of irrigation fluid delivered to the patientduring treatment.

In a second step, shown in FIG. 15B, ablation energy is directed to atleast some of the outer portion 138 of the ablation electrode 124 incontact with the tissue “T”. As the ablation energy is delivered to theablation electrode 124, the pressure of the irrigation fluid can beincreased, resulting in a higher pressure flow directed from theirrigation element 128 toward the inner portion 136 of the ablationelectrode 124. The higher flow of irrigation fluid at the inner portion136 can result in turbulent flow which, compared to laminar flow, canimprove heat transfer away from the ablation electrode 124. For example,each jet of irrigation fluid issuing from the irrigation element 128 canhave a Reynolds number above about 2000 (e.g., greater than about 2300)at the inner portion 136 of the ablation electrode 124 when thedeformable portion 142 is in the uncompressed state.

While certain embodiments have been described, other embodiments areadditionally or alternatively possible.

For example, while forming the deformable portion of an ablationelectrode has been described as including removal of material from aflat sheet, other methods of forming a deformable portion of an ablationelectrode are additionally or alternatively possible. For example, adeformable portion of an ablation electrode can be formed by removingmaterial (e.g., by laser cutting) from a tube of material (e.g., a tubeof nitinol). With the material removed, the tube can be bent into asubstantially enclosed shape such as the substantially spherical shapesdescribed herein.

As another example, while the deformable portion of an ablationelectrode has been described as being formed by removing material from aunitary structure of material (e.g., from a plate and/or from a tube),other methods of forming a deformable portion of an ablation electrodeare additionally or alternatively possible. For example, a deformableportion of an ablation electrode can include a mesh and/or a braidhaving greater than about 5 percent and less than about 50 percent openarea along an inner portion of the ablation electrode. The mesh materialcan be, for example, nitinol. It should be appreciated that this meshand/or braided portion of the ablation electrode can move between acompressed and uncompressed state.

As yet another example, while an ablation electrode has been describedas having a deformable portion, along which sensors are disposed fordetermining displacement of the deformable portion, other configurationsfor determining displacement are additionally or alternatively possible.For example, a plurality of coils can be disposed along a deformableportion of an ablation electrode. In use, some coils in the pluralitycan be used to emit a magnetic field while other coils in the pluralitycan be used to measure the resultant magnetic field. The signalsmeasured can be used to determine displacement of the deformableportion. This determined displacement of the deformable portion can beused, for example, to determine shape of the deformable portion and,additionally or instead, to determine the force applied to thedeformable portion according to any one or more of the methods describedherein. Further, or instead, a plurality of ultrasound transducers canbe disposed along a deformable portion of an ablation electrode, on anirrigation element enveloped by the deformable portion, or a combinationthereof. The signals measured by the ultrasound transducers can be usedto determine displacement of the deformable portion.

As still another example, while the deformable portion of an ablationelectrode has been described as being self-expandable from thecompressed state to the uncompressed state, the deformable portion ofthe ablation electrode can be additionally or alternatively expandedand/or contracted through the application of external force. Forexample, a catheter such as any one or more of the catheters describedherein can include a sliding member extending from the handle, though acatheter shaft, and to an ablation electrode. The sliding member can becoupled (e.g., mechanically coupled) to the ablation electrode such thataxial movement of the sliding member relative to the catheter shaft canexert compression and/or expansion force on the deformable portion ofthe ablation electrode. For example, distal movement of the slidingmember can push the ablation electrode in a distal direction relative tothe catheter shaft such that the deformable portion of the ablationelectrode collapses to a compressed state (e.g., for retraction,delivery, or both). In addition, or as an alternative, proximal movementof the sliding member can pull the ablation electrode in a proximaldirection relative to the catheter shaft such that the deformableportion of the ablation electrode expands to an uncompressed state(e.g., for the delivery of treatment). In certain implementations, thesliding member can be mechanically coupled to a portion of the handlesuch that movement of the sliding member can be controlled at thehandle. It should be appreciated that the sliding member can be anelongate member (e.g., a wire) that is sufficiently flexible to bendwith movement of the shaft while being sufficiently rigid to resistbuckling or other types of deformation in response to the force requiredto move the deformable portion of the ablation electrode.

As yet another example, while the irrigation element has been describedas including a substantially rigid stem and bulb configuration, otherconfigurations of the irrigation element are additionally oralternatively possible. For example, referring now to FIG. 16, anirrigation element 128 a can include an axial portion 166 and a helicalportion 168. The irrigation element 128 a can be used in any one or moreof the catheters described herein. For example, the irrigation element128 a can be used in addition to or instead of the irrigation element128, as described with respect to FIGS. 3-5.

The axial portion 166 and the helical portion 168 are in fluidcommunication with one another and, in certain implementations, with anirrigation lumen defined by the catheter shaft. At least the helicalportion 168 and, optionally, the axial portion 166 define a plurality ofirrigation holes 134 a along at least a portion of the length of theirrigation element 128 a. In use, the delivery of irrigation fluidthrough the irrigation holes 134 a can result in an axially,circumferentially, and/or radially distributed pattern. Unless otherwiseindicated or made clear from the context, the irrigation element 128 acan be used in addition to or instead of the irrigation element 128(FIG. 3). Thus, for example, it should be understood that the irrigationelement 128 a can provide substantially uniform cooling along the innerportion 136 of the ablation electrode 124 (FIG. 3).

The irrigation holes 134 a can be similar to the irrigation holes 134defined by the irrigation element 128 (FIG. 3). For example, theirrigation holes 134 a can be the same size and shape as the irrigationholes 134 defined by the irrigation element 128. Additionally, oralternatively, the irrigation holes 134 a can have the same open area asthe irrigation holes 134 defined by the irrigation element 128.

The axial portion 166 of the irrigation element 128 can be coupled to acatheter shaft (e.g., to a distal end portion of the catheter shaft suchas the distal end portion 132 of the catheter shaft 122 described withrespect to FIGS. 2-4). Additionally, or alternatively, the axial portion166 can extend distally from the catheter shaft. For example, the axialportion 166 can extend distally from the catheter shaft, along an axisdefined by the irrigation lumen.

In general, the helical portion 168 extends in a radial direction awayfrom the axial portion 166. In certain implementations, a maximum radialdimension of the helical portion 168 is less than an outer diameter ofthe catheter shaft. In such implementations, the helical portion 168 canremain in the same orientation during delivery and use of the catheter(e.g., during any of the delivery and/or use methods described herein).In some implementations, however, the helical portion 168 can beresiliently flexible (e.g., a nitinol tube shape set in a helicalconfiguration) such that the maximum radial extent of the helicalportion 168 is less than an outer diameter of the catheter shaft duringdelivery to the treatment site and expands such that the maximum radialextent of the helical portion 168 is greater than the outer diameter ofthe catheter shaft in a deployed position. It should be appreciatedthat, in the deployed position, the helical portion can be positionedcloser to the inner surface of an ablation electrode, which canfacilitate delivery of irrigation fluid to the inner surface of theablation electrode.

In addition to extending in a radial direction away from the cathetershaft, the helical portion 168 extends in a circumferential directionrelative to the axial portion 166. For example, the helical portion 168can extend circumferentially about the axial portion 166 through atleast one revolution. Such circumferential extension of the helicalportion through at least one revolution can facilitate substantiallyuniform dispersion of irrigation fluid about an inner surface of asubstantially spherical ablation electrode enveloping the helicalportion 168.

Optionally, the helical portion 168 can further extend in an axialdirection relative to the axial portion 166. Thus, as used herein, thehelical portion 168 should be understood, in the most general sense, toinclude any of various different helical patterns that are substantiallyplanar and/or various different helical patterns that extend axiallyrelative to the axial portion 166.

As another example, while the irrigation element has been described ashaving a discrete number of uniform irrigation holes, otherimplementations are additionally or alternatively possible. For example,referring now to FIG. 17, an irrigation element 128 b can be a porousmembrane defining a plurality of openings 170. In general, the pluralityof openings 170 are a property of the material forming the irrigationelement 128 c and are, therefore, distributed (e.g., non-uniformlydistributed and/or uniformly distributed) along the entire surface ofthe irrigation element 128 b. Because the openings 170 are a property ofthe material forming the irrigation element 128 b, the plurality ofopenings 170 can be substantially smaller than irrigation holes formedin an irrigation element through laser drilling or other similarsecondary processes. Unless otherwise indicated or made clear from thecontext, the irrigation element 128 b can be used in addition to orinstead of the irrigation element 128 (FIG. 3) and/or the irrigationelement 128 a (FIG. 16). Thus, for example, it should be understood thatthe irrigation element 128 b can provide substantially uniform coolingalong the inner portion 136 of the ablation electrode 124 (FIG. 3).

In certain implementations, the irrigation element 128 b can include anarrangement of one or more polymers. Such an arrangement can be porousand/or microporous and, as an example, can be formed ofpolytetrafluoroethylene (PTFE). In such implementations, the openings170 can be defined by spaces between polymeric fibers or through thepolymeric fibers themselves and are generally distributed along theentire surface of the irrigation element 128 b. It should be appreciatedthat the large number of the openings 170 and the distribution of theopenings 170 along the entire surface of the irrigation element 128 bcan produce a substantially uniform spray of irrigation fluid. Further,the large number of the openings 170 and the distribution of theopenings 170 along the entire surface of the irrigation element 128 bcan facilitate interaction of multiple different fluid jets and, thus,the development of turbulent flow of irrigation fluid.

The size and distribution of the openings 170 defined between or throughpolymeric fibers can allow the irrigation element 128 b to act as aselective filter. For example, because blood molecules are substantiallylarger than water molecules, the size (e.g., the average size) of theopenings 170 can be smaller than blood molecules but larger than watermolecules. It should be appreciated that such sizing of the openings 170can permit egress of irrigation fluid from the irrigation element 128 bwhile preventing ingress and, thus, clotting of blood molecules into theirrigation element 128 b.

The arrangement of one or more polymers of the irrigation element 128 bcan include electrospun polytetrafluorethylene and/or expandedpolytetrafluoroethylene (ePTFE). In certain implementations, thearrangement of one or more polymers is nonwoven (as shown in FIG. 17)resulting in the spacing between the fibers being substantiallynon-uniform such that the openings 170 defined by the spacing betweenthe fibers are of non-uniform size and/or non-uniform distribution. Insome implementations, the irrigation element 128 b can include a wovenor fabric arrangement of polymers through which irrigation fluid can bedirected. For example, the fabric can be formed of one or more polymersor other biocompatible materials woven together to form a substantiallyuniform porous barrier through which, in use, irrigation fluid may pass.Examples of polymers that can be arranged together into a fabricsuitable for forming the irrigation element 128 c include, but are notlimited to, one or more of the following: polyester, polypropylene,nylon, PTFE, and ePTFE.

In some implementations, the irrigation element 128 b can include anopen cell foam such that the openings 170 are defined by cells of theopen cell foam along the surface of the irrigation element 128 b. Insuch implementations, irrigation fluid can move through tortuous pathsdefined by the open cell foam until the irrigation fluid reaches theopenings 170 along the surface of the irrigation element 128 b, wherethe irrigation fluid exits the irrigation element 128 b. It should beappreciated that, in such implementations, the openings 170 aredistributed along the entire surface of the irrigation element 128 b,resulting in spray of irrigation fluid issuing from the irrigationelement 128 b in a substantially uniform and substantially turbulentpattern.

As yet another example, while irrigation elements have been described asincluding a resilient, expandable helical portion, other types ofresilient, expandable irrigation elements are additionally oralternatively possible. For example, referring now to FIGS. 18 and 19,an irrigation element 128 c can be a resilient, inflatable structure,such as balloon, disposed along a distal end portion 132′ of a cathetershaft 122′ and in fluid communication with a lumen 151′. In certainimplementations, the irrigation element 128 c and the ablation electrode124′ can each be coupled to the distal end portion 132′ of the cathetershaft 122′. Unless otherwise indicated or made clear from the context,an element designated with a primed (′) element number in FIGS. 18 and19 is similar to a corresponding element designated with an unprimednumber in other figures of the present disclosure and, thus, should beunderstood to include the features of the corresponding elementdesignated with an unprimed number. As one example, therefore, theablation electrode 124′ should be understood to correspond to theablation electrode 124 (FIG. 3), unless otherwise specified.

In certain implementations, the irrigation element 128 c is expandable.For example, the irrigation element 128 c can be uninflated and/orunderinflated in a delivery state of the distal end portion 132′ of thecatheter shaft 122′ to a treatment site according to any of the methodsdescribed herein. In such a delivery state, the irrigation element 128 ccan be delivered to the treatment site with a low profile (e.g., aprofile that is less than or equal to a maximum outer dimension of thecatheter shaft 122′). At the treatment site, the irrigation element 128c can be inflated to expand from the delivery state to an expandedstate. For example, the irrigation element 128 c can expand in a radialdirection beyond an outermost dimension of the catheter shaft 122′).

The irrigation element 128 c can be a non-compliant balloon or asemi-compliant balloon. In such implementations, the irrigation element128 c can be substantially resistant to deformation when in an inflatedstate. Thus, in instances in which the irrigation element 128 c isnon-compliant or semi-compliant, the irrigation element 128 c can resistdeformation when contacted by an inner portion 136′ of the deformableportion 142′ of the ablation electrode 124′. As compared to a compliantballoon, this resistance to deformation by the irrigation element 128 ccan facilitate, for example, control over the flow of irrigation fluidthrough the irrigation element 128 c.

In some implementations, the irrigation element 128 c is a balloonformed of one or more polymers. Polymers can be, for example,sufficiently flexible to expand from the delivery state to the expandedstate while withstanding forces created by the movement of irrigationfluid through the irrigation element 128 c. In instances in which theirrigation element 128 c is formed of one or more polymers, irrigationholes can be formed in polymers through laser drilling or other similarsecondary processes. Examples of polymers that can be used to form theirrigation element 128 c include one or more of: thermoplasticpolyurethane, silicone, poly(ethylene terephthalate), and polyetherblock amide.

The irrigation element 128 c can define a plurality of irrigation holes134 c. The irrigation holes 134 c can be similar to the irrigation holes134 defined by the irrigation element 128 (FIG. 3). For example, theirrigation holes 134 c can be the same size and shape as the irrigationholes 134 defined by the irrigation element 128. Additionally, oralternatively, the irrigation holes 134 c can have the same open area asthe irrigation holes 134 defined by the irrigation element 128.

In use, irrigation fluid can flow from the lumen 151′, into theirrigation element 128 c, and can exit the irrigation element 128 cthrough the plurality of irrigation holes 134 c. In general, theplurality of irrigation holes 134 c can have a combined area that isless than the cross-sectional area of the lumen 151′ such that fluidpressure can build in the inflatable element 128 c as the irrigationfluid moves through the irrigation element 128 c. It should beappreciated, then, that the pressure in the inflatable element 128 c,resulting from the flow of irrigation fluid through the irrigationelement 128 c, can inflate the irrigation element 128 c (e.g., from thedelivery state to the expanded state).

In certain implementations, the volume defined by an inner portion 136′of the ablation electrode 124′ in an expanded or uncompressed state islarger than the volume defined by the irrigation element 128 c in anexpanded state. Thus, for example, the inner portion 136′ of theablation electrode 124′ (e.g., along the deformable portion 142′) can bespatially separated from at least a portion of the surface area of theirrigation element 128 c when the irrigation element 128 c is in theexpanded state. This spatial separation can be advantageous, forexample, for developing turbulence of irrigation fluid issuing from theirrigation holes 134 c prior to reaching the inner portion 136′ of theablation electrode 124′. It should be appreciated that, as compared toless turbulent flow and/or laminar flow, such turbulence of the flow ofirrigation fluid at the inner portion 136′ of the ablation electrode124′ can facilitate efficient cooling of the ablation electrode 124′.

The irrigation element 128 c can be enveloped by the ablation electrode124′ in an uncompressed state to facilitate, for example, coolingsubstantially the entire inner portion 136′ of the ablation electrode124′. Additionally, or alternatively, enveloping the irrigation element128 c with the ablation electrode 124′ can reduce the likelihood ofexposing the irrigation element 128 c to undesirable forces such as, forexample, forces that can be encountered as the ablation electrode 124′and the irrigation element 128 c are moved to the treatment site.

In the expanded state, the irrigation element 128 c can include asubstantially ellipsoidal portion. As used herein, a substantiallyellipsoidal portion can include a substantially spherical shape anddeformations of a substantially spherical shape.

In certain implementations, the irrigation holes 134 c are defined onthis ellipsoidal portion of the irrigation element 128 c. Thus, in suchimplementations, the ellipsoidal portion of the irrigation element 128 ccan facilitate directing irrigation fluid in multiple, different axialand radial directions. For example, the irrigation holes 134 c can bespaced circumferentially (e.g., about the entire circumference) aboutthe ellipsoidal portion of the irrigation element 128 c such thatirrigation fluid can be directed toward the inner portion 136′ of theablation electrode 142′ along various different radial directions. As anadditional or alternative example, the irrigation holes 134 c can bespaced axially (e.g., along an entire axial dimension of the ellipsoidalportion of the irrigation element 128 c) such that the irrigation fluidcan be directed toward the inner portion 136′ of the ablation electrode142′ along proximal and/or distal axial directions.

A plurality of sensors 126′ can be supported on the deformable portion142′ of the ablation electrode 124′. In use, the plurality of sensors126′ can be used to detect deformation of the deformable portion 142′.For example, the irrigation element 128 c can include a sensor 172 andelectrical signals can be driven between the one or more electrodes onthe irrigation element 128 c and each of the plurality of sensors 126′according to any of the methods described herein.

While the plurality of sensors 126′ can be used in cooperation with thesensor 172 on the irrigation element 128 c, other configurations forsensing deformation of the deformable portion 142′ are also or insteadpossible. For example, referring now to FIGS. 20 and 21, a plurality ofsensors 174 can be supported along an ablation electrode 124″ at leastpartially enveloping an irrigation element 128 c″. Unless otherwiseindicated or made clear from the context, an element designated with adouble primed (″) element number in FIGS. 20 and 21 is similar to acorresponding element designated with an unprimed number and/or with aprimed number in other figures of the present disclosure and, thus,should be understood to include the features of the correspondingelement designated with an unprimed number and/or with a primed number.As one example, the irrigation element 128 c″ should be understood toinclude the features of the irrigation element 128 c (FIGS. 18 and 19),unless otherwise specified or made clear from the context. As anotherexample, the ablation electrode 124″ should be understood to include thefeatures of the ablation electrode 124 (FIGS. 3 and 4) and/or of theablation electrode 124′ (FIGS. 18 and 19), unless otherwise specified ormade clear from the context.

Each sensor 174 can include a flexible printed circuit and/or athermistor similar to any of the flexible printed circuits and/orthermistors described herein, including the flexible printed circuit 150and/or thermistor 152 described above with respect to FIGS. 10 and 11.

In the uncompressed state of the ablation electrode 124″, the innerportion 136″ of the ablation electrode 124″ is spatially separated froma least a portion of a surface of the irrigation element 128 c″ suchthat, for example, at least one of the plurality of sensors 174 is notin contact with the irrigation element 128 c″. In certainimplementations, the ablation electrode 124″ in the uncompressed stateis not in contact with any of the plurality of sensors 174. That is, insuch implementations in which the ablation electrode 124″, in theuncompressed state, is spatially separated from one or more of thesensors 126″, the default arrangement of the sensors 126″ is away fromthe irrigation element 128 c.

The ablation electrode 124″ can include a deformable portion 142″ thatis resiliently flexible from a compressed state (e.g., in which theinner portion 136″ of the ablation electrode 124″ is in contact with theirrigation element 128 c″) to an uncompressed state (e.g., in which theinner portion 136″ of the ablation electrode 124″ is spatially separatedfrom at least a portion of the surface of the irrigation element 128c″). Thus, in such implementations, deformation of the deformableportion 142″ can place one or more of the plurality of sensors 174 intocontact with the irrigation element 128 c″ and sensing this contact canbe used to determine the shape of the deformable portion 142″ inresponse to a deformation force, such as a force exerted through contactwith tissue.

The sensors 174 can be axially and/or circumferentially spaced from oneanother along the deformable portion 142″ of the ablation electrode124″. For example, a first set of the sensors 174 can be disposed distalto a second set of the sensors 174 along the inner portion 136″ of theablation electrode 124″ (e.g., along the deformable portion 142″). Itshould be appreciated that the spatial resolution of the detecteddeformation of the deformable portion 142″ can be a function of thenumber and spatial distribution of the sensors 174, with a larger numberof uniformly spaced sensors 174 generally providing increased spatialresolution as compared to a smaller number of clustered sensors 174.

In use, an electrical signal can be driven between at least one of thesensors 174 and another one of the sensors 174. Measured electricalsignals generated between at least one of the sensors 174 and another ofthe sensors 174 can be received at a processing unit such as any of theprocessing units described herein (e.g., processing unit 109 a describedwith respect to FIG. 1).

Based at least in part on the measured electrical signals generatedbetween at least one of the sensors 174 and another of the sensors 174,deformation of the deformable portion 142″ of the ablation electrode124″ can be detected. For example, as the deformable portion 142″ of theablation electrode 124″ deforms, one or more of the sensors 174 can bebrought into contact with the irrigation element 128 c″. It should beappreciated that a certain amount of force is required to deform thedeformable portion 142″ by an amount sufficient to bring the one or moresensors 174 into contact with the irrigation element 128 c″. As usedherein, this force can be considered a threshold at least in the sensethat forces below this threshold are insufficient to bring the one ormore sensors 174 into contact with the irrigation element 128 c″ and,therefore, are not detected as contact between the one or more sensors174 and the irrigation element 128 c″.

Contact between the one or more sensors 174 and the irrigation element128 c″ can be detected, for example, as a change in the measuredelectrical signal received, by the processing unit, from the respectiveone or more sensors 174. As a non-limiting example, contact between oneor more of the sensors 174 and the irrigation element 128 c can bedetected as a rise in impedance of a respective one or more electricalsignals associated with the one or more sensors 174 in contact with theirrigation element 128 c.

The detection of deformation of the deformable portion 142″ of theablation electrode 124″ can, for example, include a determination ofwhether one or more of the sensors 174 is in contact with the irrigationelement 128 c. In addition, or instead, the detection of deformation ofthe deformable portion 142″ based on the measured electrical signals caninclude a detection of a degree and/or direction of deformation of thedeformable portion 142″. That is, a degree and/or direction ofdeformation of the deformable portion 142″ can be determined based onthe number and/or position of the one or more sensors 174 detected asbeing in contact with the irrigation element 128 c.

An indication of a determined state of the deformable portion 142″ canbe sent to a graphical user interface, such as any one or more of thegraphical user interfaces described herein (e.g., the graphical userinterface 110 described with respect to FIG. 1). In certainimplementations, the degree and/or orientation of deformation of thedeformable portion 142″ can be sent to the graphical user interface. Forexample, based on which sensors 174 are detected as being in contactwith the irrigation element 128 c, a corresponding representation of thecompressed state of the deformable portion 142″ can be sent to thegraphical user interface. The corresponding representation of thecompressed state of the deformable portion 142″ can be based on, forexample, a look-up table of shapes corresponding to differentcombinations of sensors 174 detected as being in contact with theirrigation element 128 c.

An exemplary method of making a catheter including the irrigationelement 128 c″ can include coupling (e.g., using an adhesive) theirrigation element 128 c″ to a distal end portion 132″ of a cathetershaft 122″. The deformable portion 142″ can be formed according to anyone or more of the methods described herein, and the deformable portion142″ can be positioned relative to the irrigation element 128 c″ suchthat the inner portion 136″ of the ablation electrode 124″ envelops theirrigation element 128 c″. The deformable portion 142″ can be coupled tothe catheter shaft 122″ relative to the irrigation element 128 c″ suchthat, in a compressed state, the inner portion 136″ of the ablationelectrode 124″ is in contact with the irrigation element 128 c″ and, inan uncompressed state, the inner portion 136″ of the ablation electrode124″ along the deformable portion 142″ is spatially separated from theirrigation element 128 c″.

As another example, while certain arrangements of struts to form cellsalong a deformable portion of an ablation electrode have been described,other configurations are additionally or alternatively possible. Forexample, referring now to FIGS. 22 and 23, a catheter 204 can include anablation electrode 224 having struts 244 b defining a plurality of cells247, with the struts 244 b progressively ganged together in a directionfrom a proximal region to a distal region of a deformable portion 242 ofthe ablation electrode 224. For the sake of efficient and cleardescription, elements designated by 200-series element numbers in FIGS.22 and 23 are analogous to or interchangeable with elements with100-series element numbers (including primed and double-primed elementnumbers) described herein, unless otherwise explicitly indicated or madeclear from the context, and, therefore, are not described separatelyfrom counterpart elements having 100-series element numbers, except tonote differences or to describe features that are more easily understoodwith reference to FIGS. 22 and 23. Thus, for example, catheter 204 inFIGS. 22 and 23 should generally be understood to be analogous to thecatheter 104 (FIGS. 1-4), unless otherwise explicitly indicated or madeclear from the context.

As used herein, a progressively ganged together configuration of thestruts 244 b can include an arrangement of the struts 244 b in which thenumber of cells 247 in the plurality of cells 247 decreases in a givendirection. Thus, for example, the struts 244 b can be progressivelyganged together in the direction toward the distal end of the deformableportion 242 such that the number of cells 247 defined by the strutsdecreases in the direction toward the distal end of the deformableportion 242. Thus, as compared to a configuration in which struts areuniformly disposed about a shape, the closed end of the deformableportion 242 of the ablation electrode 224 can be formed by joiningtogether relatively few of the struts 244 b. This can be advantageouswith respect to, for example, achieving acceptable manufacturingtolerances or, further or instead, facilitating substantially uniformdistribution of current density along the deformable portion 242.

In some implementations, the cells in the plurality of cells 247 can bebounded by different numbers of struts 244 b, which can facilitateachieving a target distribution of current density along the deformableportion 242. For example, a first set of cells of the plurality of cells247 can be bounded by struts 244 b defining eyelets (e.g., eyelets 157in FIG. 12B), and a second set of cells 247 can be bounded by fewerstruts than the first set of cells. For example, the first set of cellsof the plurality of cells 247 can be bounded by at least four struts 244b.

In certain implementations, at least some of the cells of the pluralityof cells 247 are symmetric. Such symmetry can, for example, facilitateachieving substantially uniform current density in a deformable portion242 of the ablation electrode 224. Additionally, or alternatively, suchsymmetry can be useful for achieving suitable compressibility of thedeformable portion for delivery to a treatment site (e.g., through asheath) while also achieving suitable expansion of the deformableportion for use at the treatment site.

At least some of the cells 247 can have mirror symmetry. As used herein,a mirror symmetric shape includes a shape that is substantiallysymmetric about a plane intersecting the shape, with the substantialsymmetry allowing for the presence or absence of a sensor 226 on one orboth sides of the plane intersecting the shape. For example, at leastsome of the cells 247 can have mirror symmetry about a respective mirrorsymmetry plane passing through the respective cell 247 and containing acenter axis C_(L)′-C_(L)′ defined by a catheter shaft 222 and extendingfrom a proximal end portion to a distal end portion of the cathetershaft 222. In the side view shown in FIG. 23, a mirror symmetry planefor some of the cells of the plurality of cells 247 is directedperpendicularly into the page and passes through the center axisC_(L)′-C_(L)′. Additionally, or alternatively, it should be appreciatedthat the overall deformable portion 242 of the ablation electrode 224can be symmetric about a plane including the center axis C_(L)′-C_(L)′,such as the plane directed perpendicularly into the page and passingthrough the center axis C_(L)′-C_(L)′.

The mirror symmetry of at least some of the cells of the plurality ofcells 247 and/or the overall deformable portion 242 can be useful, forexample, for uniform distribution of current density. Additionally, oralternatively, symmetry can facilitate expansion and contraction of thedeformable portion 242 of the ablation electrode 224 in a predictableand repeatable manner (e.g., with little to no plastic deformation). Forexample, each of the cells of the plurality of cells 247 can besymmetric about its respective symmetry plane in the compressed stateand in the uncompressed state of the deformable portion 242 of theablation electrode 224. With such symmetry in the compressed state andin the uncompressed state of the deformable portion 242, the deformableportion 242 can expand with little to no circumferential translation ofthe deformable portion 242 during expansion, which can facilitateaccurate knowledge of the position of the deformable portion 242 duringdelivery and deployment of the deformable portion 242.

The catheter 204 can be formed according to any one or more of thevarious different methods described herein. For example, the ablationelectrode 224 can be formed from a flat sheet or from a tube, asdescribed herein, such that the ablation electrode 224 has two openends. A fastener 241 b can be inserted through an end of at least someof the struts 244 b according to any of the various different methodsdescribed herein to couple ends of the struts 244 b to close one of thetwo open ends of the ablation electrode 224. An open end of ablationelectrode 224 (e.g., an end opposite the fastener 241 b) can be coupledto a distal end portion 232 of the catheter shaft 222 to form thecatheter 204.

The following simulation and experiment describe the uniformity ofcurrent density associated with the ablation electrode 224 in theuncompressed state. It is to be understood that the simulation andexperiment described below are set forth by way of example only, andnothing in the simulation or experiment shall be construed as alimitation on the overall scope of this disclosure.

Referring now to FIG. 24, current density through the deformable portion242 of the ablation electrode 224 (FIG. 22) in the uncompressed statewas simulated using a finite difference method. In the simulation, theablation electrode 224 was assumed to have uniform voltage (e.g., 1 V),with the medium set at uniform resistivity. The return electrode wasassumed to be the edge of the domain and was set to another uniformvoltage (e.g., 0 V). It is believed that the variation in simulatedcurrent density along a trajectory (shown as the arc extending fromposition 0 to position 450) at a fixed distance away from an outersurface of the deformable portion 242 is a proxy for the actualvariation in current density along the respective trajectory of thedeformable portion 242.

Referring now to FIGS. 24 and 25, the simulated current density throughthe deformable portion 242 varies by less than about ±10 percent alongthe trajectory at 1 mm away from an outer surface of the deformableportion 242 in the uncompressed state. Thus, the current density at afixed distance near the deformable portion 242 in the uncompressed stateis believed to be relatively uniform. Thus, more generally, currentdensity near the surface of the deformable portion 242 is substantiallyinsensitive to the orientation of the deformable portion 242 relative totissue. Further, given that the deformable portion 242 in the expandedstate is larger than a maximum lateral dimension of the catheter shaft222 (FIG. 22), the deformable portion 242 can reliably deliver widelesions in any of various different orientations relative to tissue.This can be useful, for example, for reducing treatment time and/orincreasing the likelihood that applied ablation energy is sufficient totreat a targeted arrhythmia.

While the results shown in FIG. 25 are based on a simulation using afinite difference method, the general observations drawn from thesesimulations are supported by the experimental results described below.

FIG. 26 is a graph of depth of lesions applied to chicken breast meatusing the ablation electrode 224 in axial and lateral orientationsrelative to the chicken breast meat. Each lesion was performed onchicken breast meat and 0.45% saline solution at body temperature and,for each lesion, the deformable portion 242 of the ablation electrode224 was in contact with the chicken breast meat with 10 g of force and 8ml/min of irrigation was used. For each ablation, 2 amperes weredelivered to the tissue through the deformable portion 242 (FIG. 22) forten seconds. Lesion depth was determined using a ruler to measure thedepth of tissue discolored from pink to white.

Five of the lesions were created with the deformable portion 242 (FIG.22) in an axial orientation in which the catheter shaft 222 (FIG. 22)was perpendicular to the chicken breast, and five of the lesions werecreated with the deformable portion 242 in a lateral orientationperpendicular to the axial orientation. As shown in FIG. 26, althoughthe lesions were created using different orientations, the lesion depthswere similar, with lesion depth varying by less than about ±20 percent,indicating that the amount of energy ablating tissue in bothorientations is similar. This experimental finding is consistent withthe results of the simulation. That is, lesions corresponding tomultiple different angles between the deformable portion 242 (FIG. 22)and tissue have similar depth at each of the multiple different angles.Such uniform distribution of current density can facilitate controllinglesion size, which can be particularly useful for ablating thin tissue.

Referring again to FIGS. 22 and 23, an irrigation element 228 isenveloped by the deformable portion 242 of the ablation electrode 224such that the deformable portion 242 forms an enclosure about theirrigation element 228. The irrigation element 228 can be any of thevarious different irrigation elements described herein and can be influid communication with a catheter shaft 222. For example, theirrigation element 228 can be disposed substantially along the centeraxis C_(L)′-C_(L)′, can extend distally from a distal end portion 232 ofthe catheter shaft 222, and, also or instead, can define a plurality ofirrigation holes 234 disposed along the irrigation element 228 to directirrigation fluid toward the deformable portion 242 of the ablationelectrode 224. Additionally, or alternatively, a center electrode 235can be disposed along the irrigation element 228 and directly orindirectly coupled to the distal end portion 232 of the catheter shaft222.

In the absence of force applied to the deformable portion 242 of theablation electrode 224, the center electrode 235 is spaced apart fromthe sensors 226. As the deformable portion 242 is brought into contactwith tissue through application of force applied to the deformableportion 242, it should be appreciated that, independent of orientationof the deformable portion 242 relative to tissue, the deformable portion242, and thus the sensors 226, makes initial contact with the tissuebefore the center electrode 235 makes initial contact with the tissue.In certain implementations, the center electrode 235 remains spaced fromtissue under normal operation. That is, the deformable portion 242 ofthe ablation electrode 224 can be sufficiently rigid to maintain spacingof the center electrode 235 from tissue under a normal range of contactforces, which are less than about 100 g (e.g., less than about 50 g).

Electrical activity detected (e.g., passively detected) by the centerelectrode 235 and the sensors 226 (acting as surface electrodes) canform the basis of respective electrograms associated with each uniquepairing of the center electrode 235 and the sensors 226. For example, inimplementations in which there are six sensors 226, the center electrode235 can form six electrode pairs with the sensors 226 which, in turn,form the basis for six respective electrograms.

An electrogram formed by electrical signals received from eachrespective electrode pair (i.e., the center electrode 235 and arespective one of the sensors 226) can be generated through any ofvarious different methods. In general, an electrogram associated with arespective electrode pair can be based on a difference between thesignals from the electrodes in the pair and, thus more specifically, canbe based on a difference between an electrical signal received from thecenter electrode 235 and an electrical signal received from a respectiveone of the sensors 226. Such an electrogram can be filtered or otherwisefurther processed to reduce noise and/or to emphasize cardiac electricalactivity, for example.

Because the center electrode 235 remains spaced at an intermediatedistance from the sensors 226 and tissue in the range of forcesexperienced through contact between tissue and the deformable portion242 of the ablation electrode 224, the electrogram formed from eachelectrode pair can advantageously be a near-unipolar electrogram. Asused herein, a near-unipolar electrogram includes an electrogram formedbased on the difference between two electrodes that are greater thanabout 2 mm apart and less than about 6 mm apart and oriented such thatone of the electrodes remains spaced away from tissue. In certainimplementations, in the absence of force applied to the deformableportion 242 of the ablation electrode 224, the center electrode 235 isspaced apart from the sensors 226 by distance greater than about 2 mmand less than about 6 mm.

The near-unipolar electrograms associated with the center electrode 235spaced from the sensors 226 can provide certain advantages over unipolarconfigurations (i.e., configurations having electrode spacing greaterthan 6 mm) and over bipolar configurations (i.e., configurations havingelectrode spacing equal to or less than 2.5 mm and/or allowing bothelectrodes to be spaced close to tissue). For example, as compared tounipolar electrograms, the near-unipolar electrograms formed based onsignals received from the center electrode 235 and the sensors 226 areless noisy and, additionally or alternatively, less susceptible tofar-field interference from electrical activity away from the tissue ofinterest. Also, as compared to unipolar electrograms, a near-unipolarelectrogram does not require a reference electrode on a separatecatheter or other device. As a further or alternative example, ascompared to bipolar electrograms, a near-unipolar electrogram formedbased on signals received from the center electrode 235 and the sensors226 is generated from an electrode pair with only one electrode in theelectrode pair in contact with tissue such that the resultingelectrogram waveform arises from one tissue site, making it less complexto interpret. Also, or instead, as compared to bipolar electrogramsgenerated from a pair of electrodes in contact with tissue, the signalof a near-unipolar electrogram formed based on signals received from thecenter electrode 235 and the sensor 226 in contact with tissue can havea more consistent morphology and/or a larger amplitude at least becausethe center electrode 235 is always oriented away from tissue as comparedto the sensor 226 in the electrode pair touching tissue.

The sensors 226 can be any of the various different sensors describedherein and, in addition or in the alternative, can be arranged on thedeformable portion 242 of the ablation electrode 224 according to any ofthe various different arrangements described here. For example, in theabsence of external force applied to the deformable portion 242 of theablation electrode 224 enveloping the center electrode 235, the sensors226 can be noncoplanar relative to one another. It should be appreciatedthat, as compared to a planar arrangement, the electrograms generatedfrom the sensors 226 arranged in such a noncoplanar configuration can beuseful for providing improved directional information regardingelectrical activity in tissue.

The sensors 226 can be electrically isolated from the deformable portion242 of the ablation electrode 224 with the sensors 226, acting assurface electrodes, passively detecting electrical activity in tissue inproximity to each respective sensor 226 without interference from thedeformable portion 242 of the ablation electrode 224. At least some ofthe sensors 226 can be disposed on an outer portion of the deformableportion 242 of the ablation electrode 224 with the deformable portion242 of the ablation electrode between the center electrode 235 and atleast a portion of each respective one of the sensors 226 on the outerportion. Additionally, or alternatively, at least some of the sensors226 can be disposed on an inner portion of the deformable portion 242 ofthe ablation electrode 224. In such implementations, each sensor 226 canbe in proximity to tissue without touching tissue as the deformableportion 242 of the ablation electrode 224 touches tissue.

Referring now to FIGS. 1, 22, and 23, the catheter 204 can replace thecatheter 104 in FIG. 1. Accordingly, electrical signals from the sensors226 and the center electrode 235 can be directed to the catheterinterface unit 108. For example, the signals can be sent to anelectrical input stage associated with the catheter interface unit 108.In certain implementations, the difference between electrical signals isdetermined through electronic circuitry (e.g., a voltage amplifier witha differential input). Additionally, or alternatively, the differencebetween electrical signals can be determined by the processing unit 109a of the catheter interface unit 108.

In general, the storage medium 109 b of the catheter interface unit 108can have stored thereon computer-executable instructions for causing theprocessing unit 109 a to acquire a plurality of electrograms (e.g., anelectrogram for each electrode pair formed by the center electrode 235and each respective sensor 226). The storage medium 109 b be can, alsoor instead, have stored thereon instructions for causing the processingunit 109 a to display a representation of at least one of the pluralityof electrograms on the graphical user interface 110. In certainimplementations, the storage medium 109 b can have stored thereoninstructions for causing the processing unit 109 a to determine avoltage map associated with the plurality of electrograms, the voltagemap corresponding, for example, to electrical activity of a heart of apatient. In some implementations, the storage medium 109 b can havestored thereon instructions for causing the processing unit 109 a todisplay the voltage map on the graphical user interface 110. Thedisplayed electrograms, alone or in combination with a displayed voltagemap, can be useful for selectively treating tissue of the heart (e.g.,delivering ablation energy from the deformable portion 242 of theablation electrode 224 to tissue in a cavity of the heart).

While the center electrode 235 has been described as being disposed onthe irrigation element 228, it should be appreciated that the centerelectrode 235 can additionally or alternatively be located at any ofvarious different positions within the deformable portion 242 of theablation electrode 224. For example, the center electrode 235 can bepositioned on the distal end portion 232 of the catheter shaft 222.Additionally, or alternatively, the irrigation element 228 itself can beused as a center electrode.

Referring now to FIGS. 1, 22, 23, and 27, various different parametersof the RF energy delivered by the ablation generator 116 to the ablationelectrode 224 (e.g., at an interface between endocardial tissue andblood in a heart cavity of a patient) can be controlled during a periodof lesion formation to achieve desired characteristics of the resultinglesions formed in tissue in contact with the ablation electrode 224(e.g., in contact with the deformable portion 242 of the ablationelectrode 224). For example, as described in greater detail below, theRF energy delivered by the ablation electrode 224 to the tissue can becontrolled to interact advantageously with local heat transfer patternsto produce large lesions.

The RF energy, shown as electric current in FIG. 27, delivered to theablation electrode 224 can be pulsed to cycle (e.g., repeatedly) betweena first energy phase 310 and a second energy phase 320 during a periodof lesion formation (e.g., when the ablation electrode 224 is in contactwith tissue). For the sake of clarity of explanation, pulsation of RFenergy is described herein with reference to electric current. It shouldbe readily understood, however, that any one or more of the systems andmethods described herein can additionally, or alternatively, includepulsation of voltage, unless otherwise specified or made clear from thecontext.

The first energy phase 310 is greater than the second energy phase 320such that repeated cycling between the first energy phase 310 and thesecond energy phase 320 results in a pulse wave 330 having an amplitude332 and a period 334. One or more of the amplitude 332 and the period334 of the pulse wave 330 can be varied during the formation of a givenlesion to control, for example, the size of the lesion produced by theintroduction of the RF energy into the tissue. Additionally, oralternatively, the percentage of time spent in the first energy phase310 relative to the second energy phase 320 can be varied to achieved atarget duty cycle of energy delivered to tissue at a treatment site. Incertain instances, however, the amplitude 332, the period 334, and/orthe duty cycle of the pulse wave 330 can be fixed, which can be useful,for example, for simplifying the software and/or hardware used togenerate the pulse wave 330. Additionally, or alternatively, theparameters of the pulse wave 330 during the first energy phase 310and/or the second energy phase 320 can be a function of a sensedparameter, a computed parameter, or a combination thereof. As anexample, the energy delivered to the ablation electrode 224 during thefirst energy phase 310 can be controlled to maintain a known temperature(e.g., a temperature of about 70° C.) for a given amount of time and,because the first energy phase 310 is greater than the second energyphase 320, the duration of the second energy phase 320 can be controlledto maintain temperature of the tissue below a predetermined thresholdfor a given amount of time.

The repeated cycling between the first energy phase 310 and the secondenergy phase 320 can result in corresponding cycling of ablation energydelivered to tissue in contact with the ablation electrode 224. Morespecifically, the first energy phase 310 can correspond to energysuitable to ablate tissue in contact with the ablation electrode 224,and the second energy phase 320 can correspond to an energy level thatdoes not result in ablation of the same tissue in contact with theablation electrode 224. For example, the second energy phase 320 cancorrespond to an “off” state in which no energy is delivered to theablation electrode 224. Additionally, or alternatively, the secondenergy phase 320 can correspond to a low energy state, such as a statethat might be useful for sensing tissue parameters.

In general, the hottest point in tissue receiving RF energy from theablation electrode 224 is a point away from the surface in contact withthe ablation electrode 224 because the surface in contact with theablation electrode 224 is irrigated through the movement of blood,irrigation fluid, or both. Without wishing to be bound by theory, and asdescribed in greater detail below, it is believed that pulsed RF energyproduces lesion sizes larger than those produced by non-pulsed RF energyof the same amplitude at least because, as compared to cooling thatoccurs when non-pulsed RF energy of the same amplitude is used, thehottest point in the tissue is cooled differently when pulsed RF energyis used to ablate tissue.

Referring now to FIG. 28, when RF energy is delivered to the ablationelectrode 224, heat is generated in the blood, at the surface of thetissue “T,” and within the tissue “T,” through, for example, Jouleheating. In general, more heat is generated near the ablation electrode224, where current density is highest, and generated heat decreases withdistance away from the ablation electrode. In the case in whichnon-pulsed RF energy is directed from the ablation electrode 224 intothe tissue “T,” heat is transferred into a portion of the tissue “T”defined by a lesion boundary “L” at a rate, O_(in), while heat istransferred away from the portion of tissue “T” defined by the lesionboundary “L” at a rate, Q_(out). The rate of heat carried away, Q_(out),can be a combination of conduction below the surface of tissue “T” andconvective cooling by blood and/or irrigation fluid moving past thesurface of tissue “T” in the anatomic structure. Initially, Q_(in) isgreater than Q_(out) such that the lesion boundary “L” will continue togrow (e.g., move away from the surface of tissue “T”) as non-pulsed RFenergy is directed into the tissue “T.” Under conditions in which thenon-pulsed RF energy is applied by the ablation electrode 224 to tissue“T” for a sufficiently long period of time (e.g., about 1-2 minutes incardiac tissue), however, thermal equilibrium is eventually reached intissue “T.” As used herein, such a thermal equilibrium conditionincludes a condition in which the heat transfer rate, O_(in), into thetissue within the lesion boundary “L” substantially equals the heattransfer rate away, Q_(out), from the tissue within the lesion boundary“L”. Once thermal equilibrium is established in tissue “T,” the deliveryof more non-pulsed RF energy of the same amplitude will not result insubstantial further propagation of the lesion boundary “L.” Thus, at agiven amplitude of non-pulsed RF energy delivered to tissue “T” by theablation electrode 224, the lesion boundary “L” has an approximatemaximum depth and maximum width under conditions in which thermalequilibrium is established in tissue “T.”

In general, the maximum depth and maximum width of the lesion boundary“L” is limited by the amplitude of the non-pulsed RF energy that can bedelivered safely to tissue “T” without damaging tissue “T” (e.g.,without causing steam-pop to occur in tissue “T”) at a hottest point “H”and without overheating blood (e.g., without causing thrombusformation). The surface of tissue “T” is cooled by the flow of bloodand/or irrigation fluid and, thus, the hottest point “H” is generally ata position below the surface of tissue “T.” The temperature of thesurface of tissue “T” can be used as a proxy for the temperature of thehottest point “H” such that, by maintaining temperature of the surfaceof tissue “T” below a threshold, the hottest point “H” can be maintainedbelow a temperature associated with tissue damage. That is, temperaturefeedback from the surface of tissue “T” (e.g., from one or more sensors246 carried by the ablation electrode 224) can be used as a feedbackparameter to control the amplitude of the non-pulsed RF energy appliedto tissue “T” such that the temperature of the hottest point “H” oftissue “T” can be maintained at a safe temperature.

Referring now to FIGS. 27, 29A, and 29B, RF energy delivered to tissue“T” by ablation electrode 224 can be pulsed to cycle repeatedly betweenthe first energy phase 310 and the second energy phase 320. In general,the pulsation of RF energy delivered to tissue “T” by the ablationelectrode 224 can decouple lesion size from thermal equilibrium andtemperature constraints associated with non-pulsed RF energy. As shownin FIGS. 29A and 29B, a point “K” below the surface of tissue “T” is thehottest point during delivery of pulsed RF energy, and a point “P” isrepresentative of cooler tissue further into tissue “T” than the point“K.” As described in greater detail below, the heat directed at thepoint “K” advantageously changes as the RF energy is pulsed from thefirst energy phase 310 to the second energy phase 320, with theresulting change facilitating delivery of thermal ablation energy to thepoint “P” while the temperature of the point “K” is maintained at a safetemperature. More generally, the change in the heat directed at thepoint “K” as the RF energy is pulsed from the first energy phase 310 tothe second energy phase 320 can facilitate the creation of lesionslarger than those achievable by delivering of non-pulsed RF energy untilthermal equilibrium is established in tissue “T.”

During the first energy phase 310 of pulsed RF energy delivered totissue “T,” shown in FIG. 29A, heat is directed into point “K” at arate, Q_(in) _(_) _(p), greater than a rate at which heat is carriedaway from tissue “T” and away from point “K,” Q_(out) _(_) _(p). Therate of heat carried away from point “K,” Q_(out) _(_) _(p), is afunction of conduction from point “K” to cooler portions of tissue “T”and convective cooling by fluid moving past the surface of tissue “T.”As described in greater detail below, the convective cooling of thesurface of tissue “T” can be achieved through the flow of blood past thesurface of tissue “T” and, additionally or alternatively, through theflow of irrigation fluid (e.g., saline) delivered by the irrigationelement 228 toward the surface of tissue “T” according to any one ormore of the systems and methods of irrigation described herein.

In general, the duration of the first energy phase 310 is less than aduration required for establishing thermal equilibrium at point “K” and,thus, the temperature of point “K” can increase during the duration ofthe first energy phase 310. For example, amplitude and/or duration ofthe RF energy directed into tissue “T” during the first energy phase 310can be such that the point “K” and, optionally, nearby tissue (e.g.,tissue at a point “P”) undergoes thermal ablation during the firstenergy phase 310.

During the second energy phase 320 of pulsed RF energy delivered totissue “T,” shown in FIG. 29B, heat directed into point “K” can besufficiently low (e.g., approximately zero) such that point “K”undergoes net cooling by a combination of heat conducted into coolerportions (e.g., the point “P”) of tissue “T” and convective coolingthrough blood, irrigation fluid, or a combination thereof moving pastthe surface of tissue “T.” For example, during the second energy phase320, the point “K” can be cooled as heat moves into the point “P” fromthe point “K” through conductive cooling. Further, or in thealternative, because the distance between the point “K” and the surfaceof tissue “T” is less than the distance between the point “P” and thesurface of tissue “T,” the point “K” undergoes a greater amount ofconvective cooling than the point “P” during the second energy phase320. Thus, the point “K” cools more rapidly than the point “P” duringthe second energy phase 320.

In general, because the temperature of the point “K” is a limitingfactor in the amount of heat that can be safely provided to tissue “T,”the preferential cooling of the point “K” during the second energy phase320 can facilitate delivery of more heat to the point “P” during thefirst phase 310 of pulsed RF energy than would otherwise be possiblewithout damaging the tissue “T” at the point “K.” The pulsed RF energycan be cycled between the first energy phase 310 and the second energyphase 320 to deliver additional heat to the point “P” without exceedinga threshold temperature at the point “K.” It should be appreciated thata higher temperature at the point “P” results in higher temperatures intissue “T” adjacent to the point “P” and, thus, more generally, resultsin lesion sizes larger than those achievable with non-pulsed RF energy.

Referring now to FIGS. 1, 22, 23, and 27, the ablation electrode 224 canbe positioned in an anatomic structure, at an interface between tissueand blood (e.g., at an interface between endocardial tissue and blood ina heart cavity of a patient) such that fluid (e.g., blood, irrigationfluid, or a combination thereof) in the anatomic structure can move pastthe ablation electrode 224 at the interface to cool the ablationelectrode 224, according to any of the various different methodsdescribed herein, during a period of lesion formation. For example, thestorage medium 109 b can have stored thereon computer executableinstructions for causing the processing unit 109 a to control theablation generator 116 to pulse the RF energy delivered from theablation generator 116 to the ablation electrode 224 according to anyone or more of the various different methods described herein.Additionally, or alternatively, it should be appreciated that theablation generator 116 can include circuitry to pulse the RF energydelivered from the ablation generator 116 to the ablation electrode 224according to any one or more of the various different methods describedherein. Unless otherwise indicated, each of the following exemplarymethods can be implemented using the ablation system 100 and/or one ormore components thereof, including any of the various differentcatheters described herein.

Referring now to FIG. 30, an exemplary method 350 of delivering RFenergy to target tissue can include placing 352 an ablation electrode atan interface between tissue and blood in an anatomic structure (e.g., atan interface between endocardial tissue and blood in a heart cavity of apatient), and delivering 354 RF energy to the ablation electrode at theinterface.

Placing 352 the ablation electrode at the interface between tissue andblood in the anatomic structure can include any one or more of thevarious different methods of placement of an ablation electrodedescribed herein. Thus, for example, placing 352 the ablation electrodeat the interface between tissue and blood can include moving theablation electrode into the anatomic structure by moving a distalportion of a catheter shaft, coupled to the ablation electrode, throughvasculature of the patient. Additionally, or alternatively, placing 352the ablation electrode at the interface between tissue and blood caninclude inserting a catheter into a patient according to the methodsdescribed with respect to FIGS. 13A-13E. Also, or instead, placing 352the ablation electrode at the interface between tissue and blood caninclude positioning the ablation electrode at the interface according tothe methods described with respect to FIGS. 14A-C.

Placing 352 the ablation electrode at the interface between tissue andblood can include expanding the at least a portion of the ablationelectrode, according to any one or more of the various different methodsdescribed herein, such that blood, other fluids, or a combinationthereof can move through the ablation electrode to provide cooling atthe interface between tissue and blood. In addition, or instead, placing352 the ablation electrode at the interface between tissue and blood caninclude positioning an outer surface of the ablation electrode incontact with fluid moving through the ablation electrode to providecooling at the interface between tissue and blood.

Delivering 354 pulsed RF energy to the ablation electrode at theinterface can include providing the first energy phase to ablate tissueat the interface and the second energy phase to cool tissue at theinterface. Pulsing between the first energy phase and the second energyphase can create an alternating pattern of heating and cooling at asurface of the tissue. As described with respect to FIGS. 29A and 29B,for example, such an alternating pattern of heating and cooling canresult in heat transfer patterns in tissue that facilitate formation oflesions larger than those that can otherwise be formed through the useof non-pulsed RF energy under similar conditions.

The parameters of the pulsed RF energy delivered 354 to the ablationelectrode at the interface can impact local heat transfer at theinterface and, therefore, can impact the size of the lesion formed inthe presence of such local heating. Further, it should be understoodthat the impact of these parameters on local heat transfer at theinterface can depend on a number of factors, including the type oftissue being treated, the amount of cooling provided at the interface,contact area between the ablation electrode and tissue at the interface,etc. In certain applications, however, delivering 354 pulsed RF energycan include repeatedly cycling between at least two cycles (with eachcycle including at least the first energy phase and the second energyphase) to establish a local heat transfer pattern facilitating theformation of large lesions. Additionally, or alternatively, in someapplications (e.g., ablation of endocardial tissue), the total period oflesion formation can be about 30 seconds to about three minutes.

During the first energy phase, the rate of heating of the interface bythe ablation electrode can be greater than the rate of cooling at theinterface by the fluid moving through the ablation electrode at theinterface. In general, the first energy phase can have a durationsufficient to provide significant heat to tissue such that the lesioncan progress (e.g., grow in size) during the first energy phase. Incertain applications, such as forming lesions in endocardial tissue, thefirst phase of the pulsed RF energy can be greater than about 5 secondsand less than about 20 seconds (e.g., about ten seconds).

In some implementations, the initial first energy phase can be longerthan subsequent first energy phases. For example, the duration of eachfirst energy phase can be based on exposing tissue to a predeterminedtarget temperature for a given period of time. In such instances,because the initial first energy phase is initially applied to tissue ata baseline temperature (e.g., body temperature) and subsequent firstenergy phases are applied to tissue at a temperature above the baselinetemperature, the initial first energy phase can be longer than thesubsequent first energy phases to account for the additional timerequired to heat the tissue from the baseline temperature to thepredetermined target temperature.

During the second energy phase, the rate of cooling at the interface bythe fluid moving through the ablation electrode at the interface can begreater than the rate of heating of the interface by the ablationelectrode. For example, the second energy phase can correspond to an offphase in which energy to the ablation electrode is interrupted duringthe second energy phase. Additionally, or alternatively, the secondenergy phase can correspond to low energy insufficient to heat thetissue in the presence of fluid moving through the ablation electrode.More generally, it should be appreciated that the duration of the secondenergy phase can impact the amount of cooling occurring at theinterface. As an example, the duration of the second energy phase can begreater than 0 seconds and less than about 6 seconds to achieve suitablecooling after the first energy phase of a first cycle while maintainingthe tissue at a sufficient temperature to resume ablating upon exposureto the first energy phase of a second, subsequent cycle of RF energydelivery.

In certain instances, one or both of the first energy phase and thesecond energy phase can have a predetermined duration. A predeterminedduration of one or both of the first energy phase and the second energyphase can be useful, for example, for simplifying the software and/orhardware required to control of the pulsed RF energy delivered 354 tothe interface.

In certain implementations, the exemplary method 350 can further includemonitoring 356 tissue at the interface between tissue and blood in theanatomic structure of the patient. The monitoring 356 can be based, forexample, on a signal measured at or near a point of contact between theablation electrode and tissue. For example, monitoring 356 tissue caninclude directly or indirectly detecting a change in tissue. In general,a detected change in tissue can be used as feedback to control any oneor more of various different parameters of the delivered 354 pulsed RFenergy. Examples of parameters of the pulsed RF energy that can becontrolled based at least in part on a detected change in tissue caninclude amplitude of the pulsed RF energy, duration of one or both ofthe first energy phase and the second energy phase, and duration of thelesion formation. As described in greater detail below, a detectedchange in tissue can be, additionally or alternatively, used as feedbackto control any one or more of various different parameters associatedwith delivery of irrigation fluid to the ablation electrode.

Monitoring 356 tissue at the interface of tissue and blood in theanatomic structure can include, for example, receiving one or moresignals indicative of temperature of the interface. The one or moresignals can be any of various different temperature signals describedherein. For example, the one or more signals can be received from atemperature sensor disposed at the interface (e.g., a thermistor of oneor more of the sensors 126 in FIG. 3 and/or one or more thermocouplesdisposed along a deformable portion of the ablation electrode). Incertain instances, a duration of one or more of the first energy phaseand the second energy phase can be based on the received signalindicative of temperature at the interface. For example, if the receivedsignal indicative of temperature is at or above an upper thresholdvalue, the delivered 354 pulsed RF energy can be adjusted to switch fromthe first energy phase to the second energy phase. Additionally, oralternatively, if the received signal indicative of temperature is at orbelow a lower threshold value, the delivered 354 pulsed RF energy can beadjusted to switch from the second energy phase to the first energyphase. More generally, it should be appreciated that the received signalindicative of temperature at the interface can be used to maintain thetissue within a desired temperature range for a given amount of time.

Monitoring 356 tissue at the interface of tissue and blood in theanatomic structure can, additionally or alternatively, include detectinga change in an electrical signal associated with the RF energy deliveredto the ablation electrode at the interface. The change in the electricalsignal associated with the RF energy delivered to the ablation electrodecan include, for example, detecting a change in tissue impedance, whichcan be indicative of lesion progress. In general, the impedance can be,for example, measured between two electrodes associated with theablation electrode. For example, the impedance can be measured between asurface electrode (e.g., carried on a deformable portion of the ablationelectrode) and a center electrode (e.g., carried on an irrigationelement enveloped by the deformable portion of the ablation electrode),such as any of the various different surface electrodes and centerelectrodes described herein. Additionally, or alternatively, theimpedance can be measured between the ablation electrode and an ablationreturn (e.g., a patch positioned outside of the body of the patient as areturn path). In certain instances, the duration of one or more of thefirst energy phase and the second energy phase can be based on thedetected change in the electrical signal. For example, a switch from thefirst energy phase to the second energy phase can be based on detectinga change in the electrical signal. While detecting a change in anelectrical signal has been described as detecting a change in impedance,it should be appreciated, that a change in voltage or current cansimilarly be detected as an indication of lesion progress.

Monitoring 356 tissue at the interface of tissue and blood in theanatomic structure can, further or instead, include determiningparameters of a model of the tissue and blood (e.g., one or more of athermal model and an electrical model of the tissue and blood). Such amodel can be useful, for example, for adjusting parameters of acontroller for delivery of RF energy, delivery of irrigation fluid, or acombination thereof Also, or instead, such a model can be useful forestimating temperature below the surface of the tissue, in certaininstances.

In some implementations, monitoring 356 tissue at the interface oftissue and blood in the anatomic structure can include determiningtemperature response of the tissue to RF energy delivery and,independently, determining temperature response of the tissue toirrigation rate. For example, such independent determination oftemperature response to RF energy delivery and to irrigation rate can befacilitated by delivering RF energy and irrigation fluid according toprofiles that produce step changes in RF energy and irrigation fluid atdifferent times. That is, continuing with this example, a step change inRF energy can be delivered to tissue while the irrigation rate issubstantially constant, and a step change in the irrigation rate can bedelivered to tissue while the RF energy delivered to tissue issubstantially constant. As an additional or alternative example,independent determination of temperature response to RF energy deliveryand irrigation rate can include adjusting one or more of RF energydelivery and irrigation rate with other orthogonal signals such assinusoids or combinations of sinusoids. As a more specific example, theRF energy can be adjusted above and below a nominal value using a sinewave of a first frequency, while irrigation rate can be adjusted aboveand below a nominal value using a sine wave of a second frequencydifferent from the first frequency. In general, it should be appreciatedthat, through independent variation of RF energy and irrigation rate,the impact of these parameters on tissue temperature can besubstantially isolated to facilitate accurate control of tissuetemperature.

In certain implementations, the exemplary method 350 further includesdelivering 358 irrigation fluid (e.g., saline) to the interface betweentissue and blood. In general, the irrigation fluid can be delivered 358such that fluid moving through the ablation electrode during at least aportion of the period of lesion formation includes the deliveredirrigation fluid (e.g., a combination of irrigation fluid and bloodmoves through the ablation electrode to cool the ablation electrode atthe interface). In certain implementations, delivering 358 irrigationfluid to the interface between tissue and blood can provide more coolingto the interface between tissue and blood than would otherwise beachievable through only the flow of blood past the interface betweentissue and blood. For example, the rate of cooling of the interface by acombination of blood and irrigation fluid moving through the ablationelectrode at the interface can be greater than a rate of heating of theinterface by the RF energy during the second energy phase. Additionally,or alternatively, delivering 358 irrigation fluid to the interfacebetween tissue and blood can facilitate controlling of the amount ofcooling occurring at the interface between tissue and blood, as comparedto cooling using only the flow of blood past the interface betweentissue and blood.

Delivering 358 irrigation fluid to the interface between tissue andblood can include controlling, based on the monitored 356 tissue at theinterface, a volumetric flow rate of irrigation fluid moving from asource of irrigation fluid through at least one orifice defined by anirrigation element. That is, control of the volumetric flow rate ofirrigation fluid moving from the source of irrigation fluid through atleast one orifice defined by an irrigation element can be based on acontrol loop including monitoring 356 tissue at the interface anddelivering 358 irrigation fluid at the interface. The irrigation elementcan be, for example, any one or more of the various different irrigationelements described herein. Controlling the volumetric flow rate ofirrigation fluid can include any of various different known methods ofcontrolling volumetric flow rate of a fluid, including, for example,controlling rotational speed of a peristaltic pump arranged to move theirrigation fluid from the source of irrigation fluid through the atleast one orifice defined by the irrigation element.

In certain instances, delivering 358 irrigation fluid to the interfacebetween tissue and blood can include, for example, cooling a surface ofthe ablation electrode in contact with the tissue at the interface. Ingeneral, delivering 358 irrigation fluid to the interface can includeany one or more methods of providing irrigation fluid described hereinand, thus, can include any one or more of various different methods ofdirecting irrigation fluid from an irrigation element toward an innersurface of the ablation electrode, as described herein. It should beappreciated that directing irrigation fluid from the irrigation elementtoward the inner surface of the ablation electrode can facilitateconvective cooling of the ablation electrode which, in turn, can promoteconductive cooling of the outer surface of the ablation electrode incontact with tissue. Additionally, or alternatively, at least a portionof the irrigation fluid can flow into direct contact with the outersurface of the ablation electrode in contact with tissue. It should befurther appreciated that delivering 358 irrigation fluid to theinterface can include mixing the irrigation fluid with blood movingthrough the ablation electrode and, thus, the combination of irrigationfluid and blood can provide convective cooling of the ablationelectrode.

A flow rate (e.g., a volumetric flow rate) of the irrigation fluiddelivered to the interface between tissue and blood can be controlledbased on one or more parameters associated with ablation. Such controlof the flow rate of irrigation fluid can be useful, for example, forbalancing considerations of effective cooling with those of systemiclimits of irrigation fluid in the body of the patient.

The flow rate of the irrigation fluid delivered to the interface can bebased on the RF energy delivered to the ablation electrode at theinterface. For example, the flow rate of the irrigation fluid can bechanged from a low flow rate when RF energy is not being delivered tothe ablation electrode to one or more higher flow rates when RF energyis being delivered to the ablation electrode. Additionally, oralternatively, the irrigation fluid can be pulsed between a first flowrate and a second flow rate less than the first flow rate. Thesepulsations can be timed to match substantially the cycling of the pulsedRF energy from between the first energy phase and the second energyphase. That is, the irrigation fluid can be delivered to the ablationelectrode at the first flow rate substantially in phase with the firstenergy phase and at the second volumetric flow rate substantially inphase with the second energy phase. As used herein, a volumetric flowrate substantially in phase with an energy phase includes flow thatoccurs over more than half of the duration of the corresponding energyphase. Thus, for example, a volumetric flow rate should be understood tobe substantially in phase with a corresponding energy phase whendifferences in delay between a fluid control system and an RF energycontrol system are accounted for.

The volumetric flow rate of irrigation fluid delivered to the interfacecan, further or instead, be based on sensed temperature (e.g., a sensedtemperature at the interface). In general, it should be appreciated thatcontrolling the flow rate of irrigation fluid based on sensedtemperature can be useful for reducing the likelihood of overcooling atthe onset of delivering ablation energy to tissue. More specifically,controlling the flow rate of irrigation fluid based on measuredtemperature can be useful for reducing the likelihood of cooling to suchan extent that tissue is not ablated. In implementations in which thetissue is endocardial tissue, reducing the likelihood of suchovercooling can have an associated advantage of reducing the likelihoodof unintended endocardial sparing. As used herein, sensed temperaturecan be based on one or more received signals indicative of temperaturesensed in an anatomic structure. For example, a plurality of signalsindicative of sensed temperatures can be received from respectivesensors disposed along the ablation electrode, according to any of thevarious different systems and methods described herein.

In implementations in which the flow rate of the irrigation fluid isdelivered to the interface based on sensed temperature, the volumetricflow rate of the irrigation fluid can be decreased in response to one ormore signals indicative of temperature being below a first predeterminedthreshold. Additionally, or alternatively, the volumetric flow rate canbe increased in response to the one or more signals indicative oftemperature being above a second predetermined threshold. The firstpredetermined threshold can be, for example, different from the secondpredetermined threshold. Such a difference in respective predeterminedthresholds used as the basis for increasing and decreasing thevolumetric flow rate of the irrigation fluid can be useful, for example,for introducing hysteresis into the temperature control loop. Suchhysteresis can reduce the likelihood of unintended oscillation betweenhigh and low flow rates as the tissue responds to change in thevolumetric flow rates.

It should be appreciated that the likelihood of unintended oscillationbetween high and low flow rates can further, or instead, be reduced bycontrolling a change in the volumetric flow rate (e.g., an increase, adecrease, or both) to occur over a temperature range corresponding to arange of the one or more signals indicative of temperature. As anexample of a change in the volumetric flow rate over a range oftemperatures, the volumetric flow rate can be increased according to afirst predetermined function of the one or more signals indicative oftemperature. Additionally, or alternatively, the volumetric flow ratecan be decreased according to a second predetermined function of the oneor more signals indicative of temperature. The first predeterminedfunction and the second predetermined function can be, for example, thesame over at least a portion of the temperature range associated withthe change in the volumetric flow rate. In some instances, the firstpredetermined function and the second predetermined function can bedifferent over at least a portion of the temperature range associatedwith the change in the volumetric flow rate. It should be appreciatedthat the first predetermined function and the second predeterminedfunction can be any of various different types of functions over thetemperature range and, thus, can include functions that are continuousor discontinuous (e.g., including a step change in the volumetric flowrate) over the temperature range. For example, one or more of the firstpredetermined function and the second predetermined function can bebased on, for example, a continuous time derivative of temperature.Additionally, or alternatively, one or more of the first predeterminedfunction and the second predetermined function can be based on presentand previous temperature values.

In general, the position of the maximum temperature of tissue at theinterface is not known. Accordingly, in certain implementations theexemplary method 350 can include estimating the maximum temperature. Forexample, the exemplary method 350 can include receiving a plurality ofsignals from a respective plurality of sensors disposed along theablation electrode. As compared to sensing temperature using only asingle sensor, the use of a plurality of sensors (e.g., spatiallyseparated from one another) can provide a better estimate of a maximumtemperature at the interface, even if none of the sensors is directlylocated at the position of the maximum temperature. Additionally, oralternatively, the temperature of tissue as a function of depth belowthe tissue surface can be approximated with a parameterized model, suchas a polynomial. For example, switching between the first phase and thesecond phase, with at least one of RF energy and irrigation ratediffering between the first phase and the second phase, can causetemperature measured at the surface of the tissue to change. The rate ofchange in temperature can depend, for example, on the temperature belowthe surface of the tissue. Thus, the parameters of the parameterizedmodel can be estimated using the rate of change in temperature measuredat the surface of the tissue. Continuing with this example, theparameterized model can be used to adjust energy delivery to achieve atarget temperature below the surface of the tissue.

In certain implementations, increasing the volumetric flow rate,decreasing the volumetric flow rate, or both can be based on a singlesignal of the plurality of signals, with the single signal correspondingto a maximum sensed temperature. This maximum sensed temperature, itshould be understood, may or may not correspond to the actual maximumtemperature at the interface between the ablation electrode and tissue.Nevertheless, this maximum sensed temperature can serve as a usefulproxy for the actual maximum temperature. Further, or instead, themaximum sensed temperature can advantageously serve as a robust feedbackparameter for controlling the volumetric flow rate.

In some implementations, increasing the volumetric flow rate, decreasingthe volumetric flow rate, or both can be, further or instead, based onmore complex processing of each signal of the plurality of signals. Forexample, without wishing to be bound by theory, heat transfer at theinterface of the ablation electrode and tissue occurs according toLaplace's equation of heat transfer under conditions of uniform cooling.Thus, in implementations in which this approximation of uniform coolingis a suitable approximation, processing each signal of the plurality ofsignals indicative of temperature can be based on an inverse Laplacianoperator. In such implementations, increasing the volumetric flow rate,decreasing the volumetric flow rate, or both can be based on, forexample, a maximum signal of the processed signals indicative oftemperature. Further, or instead, increasing the volumetric flow rate,decreasing the volumetric flow rate, or both can be based on one or moreof a maximum time derivative of the respective signal (e.g., in the caseof continuous time) and a time difference (e.g., in the case of discretetime).

While controlling volumetric flow has been described as being used toprovide cooling as RF energy is pulsed, it should be more generallyunderstood that the volumetric flow rate can be controlled through anyof various different combinations of monitoring 356 tissue at theinterface and delivering 358 irrigation fluid and, additionally oralternatively, as a function of any variation of the RF energy duringthe period of lesion formation. Thus, in addition to, or as analternative to, controlling the volumetric flow rate of the irrigationfluid based on RF energy pulsation, the volumetric flow rate of theirrigation fluid can be controlled to facilitate monitoring temperatureduring a portion of the period of lesion formation according to any oneor more of the methods described herein. For example, the response ofmeasured temperature to RF energy delivery can be approximated (e.g.,for small changes in RF energy delivery), as a linear system. Byswitching between the first phase and the second phase, with the RFenergy delivery different between the first phase and the second phase,the RF energy delivery input to the system can undergo a step change.Using system identification techniques known in the art, the parametersof a linear system can be estimated based on the temperature response tothis step change in RF energy. The parameters of the linear system canbe used to adjust control parameters. Additionally, or alternatively,the response of the measured temperature to irrigation flow rate can beapproximated, for small changes in irrigation flow rate, as a linearsystem. The parameters of the linear system can be estimated in asimilar way, and these parameters can be used to adjust controllerparameters.

As an example of controlling volumetric flow rate of the irrigationfluid based on RF energy pulsation, monitoring 356 tissue at theinterface can include reducing the RF energy and reducing the volumetricflow rate of the irrigation fluid can be reduced during a measurementphase of the period of the lesion formation to provide a useful tool foraccurately sensing temperature during lesion formation. In general,irrigation fluid can interfere with accurate sensing of temperature atthe interface of the ablation electrode and tissue because theirrigation fluid is cooling the area in which temperature is to bemeasured. Accordingly, reducing the volumetric flow rate of theirrigation fluid can reduce interference with temperature sensing.Because the volumetric flow rate of the irrigation fluid is reduced and,thus, less cooling is provided at the interface, the reduction in thevolumetric flow rate of the irrigation fluid can be accompanied by anassociated reduction in RF energy to decrease the likelihood ofoverheating the tissue during a temperature measurement.

With the RF energy and the volumetric flow rate of the irrigation fluidreduced during the measurement phase of the period of lesion formation,monitoring 356 tissue at the interface can include receiving one or moresignals indicative of temperature at the interface. These signals can beany one or more of the various signals described herein with respect totemperature sensing. Based on these one or more signals received duringthe measurement phase of the period of lesion formation, a temperatureat the interface can be determined according to any one or more of thevarious methods described herein. Additionally, or alternatively, thetemperature at the interface can be based on one or more signalsindicative of temperature and received during a portion of the period oflesion formation other than the measurement phase in which the RF energyand the volumetric flow of the irrigation fluid are reduced. Thedetermination of temperature can include estimation based on, forexample, a plurality of signals received from a respective plurality ofsensors disposed along the ablation electrode. The determinedtemperature, it should be appreciated, can be used as a feedbackparameter to control one or more of the volumetric flow rate of theirrigation fluid and the RF energy. For example, the determinedtemperature can form a basis for increasing or decreasing the volumetricflow rate to remain within a predetermined temperature range accordingto any of the various different methods of increasing and decreasing thevolumetric flow rate described herein. Additionally, or alternatively,the determined temperature can form a basis for switching the RF energybetween energy phases, such as the first energy phase and the secondenergy phase described herein. Further, or instead, the determinedtemperature can form a basis for titrating the RF energy delivered tothe ablation electrode. Still further or in the alternative, thedetermined temperature can be displayed on a graphical user interface(e.g., as feedback to a physician).

Following the reduction of RF energy and the volumetric flow rate of theirrigation fluid to measure temperature, the RF energy and thevolumetric flow rate of the irrigation fluid can be increased such thatlesion formation continues. To the extent it is desirable in a givenimplementation to determine temperature again during lesion formation,it should be appreciated that the RF energy and the volumetric flow rateof the irrigation fluid can again be reduced and temperature determined.More generally, it should be understood that reduction of RF energy andirrigation fluid to determine temperature during a period of lesionformation can be done multiple times, as necessary, to controltemperature at the interface of the ablation electrode and tissue.

While pulsed RF ablation has been described as being delivered throughan ablation electrode including a deformable portion expandable to havea maximum cross-sectional dimension greater than a maximumcross-sectional dimension of a catheter shaft, other implementations areadditionally or alternatively possible. For example, it should beunderstood that any one or more of the methods of delivering pulsed RFablation to tissue described herein can be carried out using an RFablation electrode with a closed tip (e.g., a tip that is impervious tothe passage of blood), unless otherwise specified or made clear from thecontext. Further, or instead, it should be understood that any one ormore of the methods of delivering pulsed RF ablation to tissue describedherein can be carried out using an RF ablation electrode having amaximum cross-sectional dimension substantially equal to a maximumcross-sectional dimension of a catheter shaft on which the RF ablationelectrode is carried. Thus, for example, lesion formation using pulsedRF ablation, as described herein, can be carried out using an RFablation electrode including a closed tip and having a maximumcross-sectional dimension substantially equal to a maximumcross-sectional dimension of a catheter shaft.

The above systems, devices, methods, processes, and the like may berealized in hardware, software, or any combination of these suitable fora particular application. The hardware may include a general-purposecomputer and/or dedicated computing device. This includes realization inone or more microprocessors, microcontrollers, embeddedmicrocontrollers, programmable digital signal processors or otherprogrammable devices or processing circuitry, along with internal and/orexternal memory. This may also, or instead, include one or moreapplication specific integrated circuits, programmable gate arrays,programmable array logic components, or any other device or devices thatmay be configured to process electronic signals.

It will further be appreciated that a realization of the processes ordevices described above may include computer-executable code createdusing a structured programming language such as C, an object orientedprogramming language such as C++, or any other high-level or low levelprogramming language (including assembly languages, hardware descriptionlanguages, and database programming languages and technologies) that maybe stored, compiled or interpreted to run on one of the above devices,as well as heterogeneous combinations of processors, processorarchitectures, or combinations of different hardware and software. Inanother aspect, the methods may be embodied in systems that perform thesteps thereof, and may be distributed across devices in a number ofways. At the same time, processing may be distributed across devicessuch as the various systems described above, or all of the functionalitymay be integrated into a dedicated, standalone device or other hardware.In another aspect, means for performing the steps associated with theprocesses described above may include any of the hardware and/orsoftware described above. All such permutations and combinations areintended to fall within the scope of the present disclosure.

Embodiments disclosed herein may include computer program productscomprising computer-executable code or computer-usable code that, whenexecuting on one or more computing devices, performs any and/or all ofthe steps thereof. The code may be stored in a non-transitory fashion ina computer memory, which may be a memory from which the program executes(such as random access memory associated with a processor), or a storagedevice such as a disk drive, flash memory or any other optical,electromagnetic, magnetic, infrared or other device or combination ofdevices.

In another aspect, any of the systems and methods described above may beembodied in any suitable transmission or propagation medium carryingcomputer-executable code and/or any inputs or outputs from same.

The method steps of the implementations described herein are intended toinclude any suitable method of causing such method steps to beperformed, consistent with the patentability of the following claims,unless a different meaning is expressly provided or otherwise clear fromthe context. So, for example performing the step of X includes anysuitable method for causing another party such as a remote user, aremote processing resource (e.g., a server or cloud computer) or amachine to perform the step of X. Similarly, performing steps X, Y and Zmay include any method of directing or controlling any combination ofsuch other individuals or resources to perform steps X, Y and Z toobtain the benefit of such steps. Thus, method steps of theimplementations described herein are intended to include any suitablemethod of causing one or more other parties or entities to perform thesteps, consistent with the patentability of the following claims, unlessa different meaning is expressly provided or otherwise clear from thecontext. Such parties or entities need not be under the direction orcontrol of any other party or entity, and need not be located within aparticular jurisdiction.

It should further be appreciated that the methods above are provided byway of example. Absent an explicit indication to the contrary, thedisclosed steps may be modified, supplemented, omitted, and/orre-ordered without departing from the scope of this disclosure.

It will be appreciated that the methods and systems described above areset forth by way of example and not of limitation. Numerous variations,additions, omissions, and other modifications will be apparent to one ofordinary skill in the art. In addition, the order or presentation ofmethod steps in the description and drawings above is not intended torequire this order of performing the recited steps unless a particularorder is expressly required or otherwise clear from the context. Thus,while particular embodiments have been shown and described, it will beapparent to those skilled in the art that various changes andmodifications in form and details may be made therein without departingfrom the spirit and scope of this disclosure and are intended to form apart of the invention as defined by the following claims, which are tobe interpreted in the broadest sense allowable by law.

What is claimed is:
 1. A method comprising: placing an ablation electrode at an interface between tissue and blood in an anatomic structure of a patient; delivering RF energy to the ablation electrode at the interface during a period of lesion formation; and delivering an irrigation fluid to the interface during at least a portion of the period of lesion formation, wherein the RF energy delivered to the ablation electrode at the interface is pulsed to cycle between a first energy phase and a second energy phase during the period of lesion formation, the RF energy in the first energy phase being greater than the RF energy in the second energy phase, and a combination of irrigation fluid and blood moves through the ablation electrode to cool the ablation electrode at the interface during the period of lesion formation.
 2. The method of claim 1, wherein a rate of cooling of the interface by the combination of blood and irrigation fluid moving through the ablation electrode at the interface is greater than a rate of heating of the interface by the RF energy during the second energy phase.
 3. The method of claim 1, wherein the second energy phase is an off phase.
 4. The method of claim 1, wherein, during the period of lesion formation, the RF energy is cycled between at least two cycles, with each cycle including a second energy phase and a first energy phase.
 5. The method of claim 1, wherein each second energy phase has a duration greater than 0 seconds and less than about 6 seconds.
 6. The method of claim 1, wherein each second energy phase has a predetermined duration.
 7. The method of claim 1, wherein each first energy phase has a predetermined duration.
 8. The method of claim 1, further comprising receiving, from a temperature sensor disposed at the interface, a signal indicative of temperature of the interface, wherein a duration of one or more of the first energy phase and the second energy phase is based on the signal indicative of temperature of the interface.
 9. The method of claim 1, further comprising detecting a change in an electrical signal associated with the RF energy delivered to the ablation electrode at the interface, wherein a duration of one or more of the first energy phase and the second energy phase is based on the detected change in the electrical signal.
 10. The method of claim 1, wherein a volumetric flow rate of the irrigation fluid is pulsed between a first volumetric flow rate and a second volumetric flow rate less than the first volumetric flow rate.
 11. The method of claim 1, wherein delivering the irrigation fluid to the interface includes mixing the irrigation fluid with blood moving through the ablation electrode at the interface.
 12. A system comprising: an ablation electrode positionable at an interface between endocardium tissue and blood in a heart cavity of a patient such that fluid in the heart cavity is movable through the ablation electrode at the interface to cool the ablation electrode during a period of lesion formation; an irrigation element defining at least one orifice positioned to direct irrigation fluid toward the ablation electrode such that the fluid movable through the ablation electrode at the interface includes irrigation fluid; a generator in electrical communication with the ablation electrode to deliver RF energy to the ablation electrode during the period of lesion formation; and a controller in communication with the generator, the controller including one or more processors and a non-transitory, computer-readable storage medium having stored thereon computer executable instructions for causing the one or more processors to control energy delivered from the generator to the ablation electrode at the interface between the endocardium tissue and blood during the period of lesion formation, wherein the RF energy delivered to the ablation electrode at the interface is pulsed to alternate between a first energy phase and a second energy phase during the period of lesion formation, the delivered RF energy in the first energy phase being greater than the delivered RF energy in the second energy phase.
 13. The system of claim 12, wherein the at least one orifice of the irrigation element is positioned to direct irrigation fluid toward the ablation electrode such that the fluid movable past the ablation electrode is a mixture of the irrigation fluid and blood in the heart cavity.
 14. The system of claim 12, wherein the controller is in communication with a source of irrigation fluid in fluid communication with the at least one orifice of the irrigation element to control a volumetric flow rate of irrigation fluid moving from the source of irrigation fluid and through the at least one orifice.
 15. The system of claim 14, wherein the computer executable instructions further including instructions for causing the one or more processors to control a volumetric flow rate of irrigation fluid delivered from the source of irrigation fluid and through the at least one orifice.
 16. The system of claim 15, wherein the computer executable instructions further include instructions for causing the one or more processors to pulse the volumetric flow rate of irrigation fluid between a first volumetric flow rate and a second volumetric flow rate less than the first volumetric flow rate.
 17. The system of claim 12, wherein each second energy phase has a duration greater than 0 seconds and less than about 6 seconds. 